Session 5: K40 Xtreeem Laser Cutter; Optimising Laser Machine Performance

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The K40 Xtreeem Laser Cutter Upgrade Series with Russ Sadler.

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Session five: Optimizing the Performance. Well, we did achieve what we set out last time.

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We’ve got the machine working now.

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But there’s still probably this session and maybe one more to finally drag this machine into working reality. Now in the last session,

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I stepped you through the vendor settings and the user settings.

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We did a few quick tests and the last test that we did, didn’t go very well.

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There was a problem at the beginning, if you remember, when the machine went BZZZZZZ before it started working.

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Now that BZZZZZZ meant that I had chosen wrong settings when I just threw some numbers into my vendor settings in my user settings.

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So today we’re going to try and explore what went wrong. Why did those numbers not work?

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So hopefully today’s session will be all about giving you an understanding of how this machine actually works.

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There will be an ideal set parameters for you to run your machine in the most efficient and fastest way possible.

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Now, as I mentioned in a very, very early session, the stepper motors on this machine are very small.

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There may be some serious limits to how fast I can actually push this machine.

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And if that does become a problem. I’ve got a turbocharger here, which I can use.

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But first of all, let’s see what the machine is capable of in its standard format, right?

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Well, let’s start at the beginning. This machine has got two ways of operating.

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One of them is cutting and the other way is engraving.

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Now I know they both burn lines, but let’s just say that we start the head, over here and we want to draw that line.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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This one, we’re going to cut. This one,

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we’re going to engrave. This is part of a series of lines that will go backwards and forwards for engraving, but I’ve only just drawn one line.

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When we come to cut. The head will move across here to that point there.

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And it will stop.

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And then it will start off again as if it was at the traffic lights, and it would gradually accelerate up to your cutting speed, which may be say.

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Ten millimeters a second. So by the time it gets to here, it might be running at 10 millimeters a second.

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Okay. And then run along that line at 10 millimeters a second.

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But before it gets to the end of that cut, it starts to slow down because there’s a corner coming up, you’ve got to put the brakes on.

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So it puts the brakes on and slows down, at that point and stops and then the head returns

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to home. Here, we’ve got accelerating from zero up to 10 millimetres a second.

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Well, when we’re engraving, we’re likely to be running at, say, 200 millimetres a second, just as an example.

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It’s a big difference from cutting. Now you will remember that we fiddled with things called the acceleration factors.

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Those acceleration factors are built into the vendor settings, so that the computer

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can understand how long it’s going to take to get to 200 millimeters a second.

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Because you don’t want a line that starts off at zero, gradually accelerates up to 200 millimetres

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a second gets to the right density and then has to slow down again.

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Now with engraving it’s different. What happens, this head then moves out to here, for example, and it says, Oh, so you want to go to 200mm a second?

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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Well, it’s going to take that amount of distance there to accelerate up to 200 a second.

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And then it’s going to take that distance there to put the brakes on and come back to zero.

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And then it’s that same distance again to accelerate up to speed.

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It’ll then draw the line, stop and decelerate.

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OK, so there is what I call dead space, dead time, dead distance.

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It’s over travel, when you’re doing engraving.

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So if you think you’ve got an A4 format machine that you could do A4 format engraving with, I’m afraid you’re going to be very,

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sorely disappointed. Because when you do engraving, you always have to leave space at the edge of your engraving to allow for this overrun.

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If you don’t, the controller will tell you that you’ve run out of space.

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It can’t run the program because either you’re too close to this edge or too close to that edge.

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So my little test pattern that went wrong was running at, I believe, five hundred millimetres a second.

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Then we were running at 200 millimetres a second. It was perfectly OK.

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It was only when we forced it up to 500 millimetres a second, that it became incorrect.

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Now I hate to throw maths and formula at you guys, because, hey, I’m not, I’m not a mathematician or a scientist.

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So what I’m trying to do here is to decode what is a very simple formula anyway,

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called Newton’s second law of motion, which basically says force equals mass times acceleration.

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How does that affect us? What the hell has that got to do with this machine?

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Well, it’s got a lot to do with this machine and a lot to do with the problem that we’re going to try and solve. Here

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we’ve got a stepper motor. “F” the force that’s driving this head backwards and forwards.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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Here we’ve got a mass. The head itself.

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I’m going to try and keep this fairly simplistic, and you have to imagine that there’s no friction in the system at all at the moment,

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but friction also adds apparent mass to the system as well.

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But let’s not get too complicated. And then we’ve got this thing called “A” acceleration.

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So here are our engraving lines that we just discussed. This line here is engraved at 400mm

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a second, 300mm, 200mm and 100mm a second. Because this up here, this axis is speed.

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This axis along here is distance. So the unit of acceleration is, for example, millimetres per second per second.

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So what this means is if I put 10 millimetres per second per second acceleration.

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It starts off zero, and after one second, it’s reached 10 millimetres a second.

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We’re starting off at 10 millimetres a second for the next second. So we add another 10 millimetres a second.

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So the speed is now increased from 10 millimetres per second to 20mm a second 30, 40, 50, 60, 70 all the way up to 400 millimetres a second.

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But it’s done it at a steady rate of acceleration, because the force is constant.

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The mass is constant.

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And so therefore the acceleration will be constant. I’ve just put numbers in here just so that you can easily see how it works.

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A mass of 10 with an acceleration of 10 will require a force of 100 to create that acceleration.

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If we reduce the force to 50 and the mass stays the same, the acceleration will be halved.

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Five. So I won’t be able to accelerate as quickly if I’ve only got half the force.

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When you understand how simple that formula is. It gives you a little bit of a visual understanding of how acceleration works.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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So what we’ve got here is distance. Remember what I said to you about this line?

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It takes a certain amount of time to build up to 100 millimeters a second,

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and then it takes a certain amount of time to decelerate from 100mm a second back to zero, speed.

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But if you take a look, this same length of line running at different speeds.

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Look, I require a much bigger distance here if I run at 400 mm a second, than if I’m running at 100mm a second.

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So I’ve got a lot more dead time, overrun when I run faster because the acceleration is constant.

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What we’re trying to do with this machine is the fastest speed that we can run and the fastest

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acceleration. So that we can get to 400 as quickly as possible and decelerate as quickly as possible.

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That way, we lose the least amount of time for every scan line. Because remember, there are thousands of scan lines in an image.

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And that’s where your cycle time is going to be won or lost. Its acceleration, not speed.

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But there is a relationship between speed and acceleration, which is even more complicated than what I’m just showing you here.

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200mm second. There wasn’t a problem. It’s the same motor, it’s the same head.

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Something has changed because it didn’t work when we put the speed up to 500 millimeters a second.

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But it did work when we ran it at 200mm a second. Why?

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Because this diagram here shows that there is no relationship between speed and acceleration.

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Provided I’ve got a constant force, I can accelerate up to whatever speed I like.

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Let’s just take a look at what this 400 300 actually means to our system.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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My little stepper motor over there has got a little wheel, say it’s about 13 millimetres diameter.

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Let’s not get too picky. It’s about 40mm circumference.

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It’s a nice round number for simple mathematical calculations. Okay, now in 100mm a second.

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We’re going to have two and a half revolutions of that wheel,

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per second. And so it goes all the way up to 400mm second where we’ll have 10 revolutions per second.

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Now when we convert those revolutions per second, by multiplying those by 60, we get speeds at 150 through two 600 RPM for the stepper motor.

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Here’s our numbers 150 RPM through to 600 RPM.

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Let’s look at this graph of the stepper motor output torque.

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This is the “F” value in our equation. And look, the force is not constant.

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The faster I run the stepper motor, the less force I get, so the less acceleration I’m going to get.

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So if I try and run this system at 400 mm a second, I’m actually running at 600 r.p.m. and at 600 rpm, it says

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0.2. When I started off at 100 millimetres a second, I was up here at nearly 0.5.

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So I’ve lost 60 per cent of my power, by the time I get to 600 RPM or 400mm a second.

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When I change the speed from 200 to 500, I’m asking the stepper motor to go beyond what it’s capable of.

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So if we decrease the acceleration to say five, then we should only require a force of 50 half the value.

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So provided we don’t go above 450 RPM, which is about 300 millimetres a second, we should find that this system is capable of doing what we want.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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500 was asking it to do too much, so speed does have an effect on the end result.

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There’s a balancing act to be performed. OK.

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How fast do you want to run? And how much acceleration for that speed,

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you can use. Because you might be able to run at that speed. But it will take this amount of time to get to that speed.

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So roughly, we’ve got one third of our cycle time in acceleration, one third doing the job and one third braking.

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So effectively, we’re only using 33 per cent of the available time to do the job, the other 66 per cent of the time is wasted.

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We’re not doing anything.

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Now, if this gets twice as long, for example, and we’ve still got room on our page to accept this distance of acceleration, then that ratio changes.

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We’ve got twice the distance, but we’ve still got the same amount of time at each end of dead time.

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So the efficiency of engraving becomes better as it becomes longer.

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My other machines are more powerful and I can use much greater accelerations.

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So basically I halved whatever I thought I could use on those machines and threw them into here.

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I’ve got no idea how these relationships combine with each other. It’ll all be just by simple experiment.

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Let’s go back to 200mm a second. I want you to just take a look carefully at

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how much of the travel there is on this pattern. How far does the head go beyond the pattern?

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Just make a note of that. Maybe two, three millimetres, maybe three millimetres? Let’s change it to 300 millimetres

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a second. Look at the amount of over travel, maybe five, six millimetres now? Because we’re running faster.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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We’ve got more over travel, more distance, the faster speed we go.

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Let’s put it up to 400 millimeters a second. It doesn’t like it, does it?

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That means that probably it’s lost its steps now.

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It doesn’t know where it is. So every time you get a problem like this, you must do a reset so the machine knows where zero, zero is.

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How do we run the machine faster? The answer is we’re going to have to slow down the acceleration.

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We don’t need to go back to the vendor settings because remember, the vendor settings are only absolute limits.

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We’re busy playing with the user settings, which are already less than the vendor settings. Processing / Sweep Parameters.

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So first of all, I must go and read. Now I can go in there and I can change that 20,000 to let’s just change that number to 10,000.

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So we’ve got a Y-Acceleration of 15,000. So we’d better change that as well to something like about 10,000, OK?

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And then we should be able to write that. And then just to make sure that the numbers have stuck, I always like to do a read again.

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And there they are, they’ve remained the same. We halved the acceleration now.

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So that means first of all, our 400mm a second should work perfectly.

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Nope! Escape / stop.

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OK, so I’ve dropped the acceleration to 5,000, speed is still 400.

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Wow. Ah, could you see how it lost steps there and changed position. So it’s still right on the edge of being unstable.

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So let’s reduce the acceleration even more, to say 3,000.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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Again, it’s lost steps because it’s jumped out of position. So we do a reset. Now it’s still running at exactly the same speed.

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But look at the casual way in which it’s doing that. Huge amount of over travel.

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We’re getting up to nearly 100 per cent over travel.

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In other words, we’re now getting to this point that I described earlier about one third of the time

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doing the job and the other two thirds of the time accelerating and decelerating.

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Let’s see what happens when we change the speed. Up to 500mm a second now?

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Yeah, you see, we’ve done it again.

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We’ve exceeded the limits. Stop. I hope

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you can see it’s not dangerous if I play with the limits and I get it wrong.

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The machine just doesn’t work. Let’s try 450 shall we? Look at the huge sweep, the dead area at the end.

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So 450 works and we’re actually, we actually are running the speed of the scan at 450,

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even though it looks as though it’s a very leisurely pace. When I look at the screen, it tells me that that took 18 seconds to produce that pattern.

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OK, so we’ve gone back to our 30,000 acceleration, 10 times greater.

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But this time we’ve reduced the speed to 200mm a second.

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I mean, the head looks as though it’s moving faster, but there’s less over travel, which gives the impression that it’s moving faster.

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Really, what I’m trying to show you is that acceleration is a very important factor.

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It plays all sorts of silly games with your mind. You think,

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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let’s wind up very fast. Thirty thousand. But hey, if I do that, I have to compromise.

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I have to use a slower speed. If I want to run fast, I have to pull my acceleration down from 30,000 to 3,000.

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But in doing so, that pattern takes 18 seconds.

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But I can run it slower, faster at eight seconds.

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Because I’ve got less over travel at the end. If you understand how it works, you can make the decision of how you want to set your machine up.

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So really, if I want to run this machine efficiently at the moment, I’m going to run it at a limit of 200 millimetres a second.

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Now, before we go anywhere else, what we’ll do, we’ll just look at the current settings on this device.

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At the moment, I’ve got this set to one amp, which is Switch one, two and three off off on.

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I’m going to change this up to 1.9 amps. I’ve got no idea whether there’s a safe limit for this motor or not,

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but we’re going to run it at one point nine amps and see what effect it has. Nothing!

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So we’re now stuck with the only real alternative. Let’s go in here and make this stepper motor bigger.

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We’ve got two problems, really. These wires go right the way back to the stepper driver, and I don’t really want to unravel all of this.

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So I’m going to take the lazy step and join the wires down here.

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There we go. So we’ve got off. Now that’s problem number one. First of all, this is a much heavier, stepper motor, probably three times the weight.

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But something else is a bit of a problem as well. And that’s this, there is no obvious fixing for it.

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I’m going to have to be a bit brutal and take that off there I think. I’m going to have a go at trying to press it off.

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OK, well, I’ve managed to fit the large motor in, it’s temporarily,

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it’s in with a, just a quick connect system. Um to prove whether or not everything works alright.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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To be honest, it’d better work OK. Because when I took this motor out, I’ve completely messed up the bearing,

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trying to get the little brass fitting off, because it was just press fitted onto there.

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So once I’d got the fitting off, I reamed It out 5mm and put an M3

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screw in it to fix it to my shaft. So I won’t have the same problem again. If this doesn’t work,

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I’m held up for a few days while I organize another motor.

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I know they’re paired up correctly, but the polarity may be wrong with the connection, so this may or may not go in the right direction.

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So when we turn it on, we shall have to be careful. We want it to go that way and hit this end stop.

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Oops so it’s going the wrong way. I will have to create an artificial zero when I turn on.

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Right, so it thinks it’s got zero there now.

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At least I’ve got the machine working, which means I can now go in and change the polarity in the vendor settings.

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Read and X-Polarity, direction polarity is positive.

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We’re going to change that to negative. We’re going to have to swap the keying over as well, I think. So,

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we’ll just write that back. Wow, that’s moving around pretty quickly, and that should be the same as the previous motor in terms of calibration.

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Turn the power on. Twenty per cent, four hundred that will do, OK.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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Oh, keying is the wrong way. That’s a small problem we can deal with. Ha ha ha, our Y is still correct, but our X is now substantially different.

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So let me just crudely measure it, so it should be a hundred.

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In fact, it’s 200. So read, into here 200 is what we finished up with.

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OK. Right? It should give us 100 by 100 now.

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There we go. So X is now ninety nine point nine two.

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I think we call that 100 shall we? So we’ve got that calibration back.

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It’s working again. Good news. I’m going to read it again.

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Put that in. And then write it back.

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So left key, right key. Go into our user settings.

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Read. And we’ve got our X and Y set to 30,000. Remember that didn’t work before, it was just, it went bonkers.

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OK, so let’s just see whether it will scan this at 30,000 by 400.

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We had to have 3,000 at 450 last time. Wow.

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Look at that. Well, he he he . So now we’re running 30,000 and 400mm a second, which we couldn’t do before because we just didn’t have the power.

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Remember, we’re really limited by speed. We’ll leave the settings at 30,000.

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Let’s push the speed up to 600.

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Let’s go to 800, so we’ve got, we’ve got some overrun there, as you can see, but it’s not terrible.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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And let’s go to a thousand. Has anybody ever seen a K40 run at a thousand millimetres a second?

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I don’t think so. Wow.

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I think we’ve got to be impressed by that. Vendor settings. Max Speed 1000, at the moment, but there’s no reason why I can’t go, read change that to 1500 and write

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that back. Now I’m allowed to go up to 1500 if I want.

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Are you curious? I certainly am. Now our speed is definitely 1500.

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OK, so 1500 does not work. Not at that acceleration.

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But of course, it may well work at a lower acceleration, but hey, I don’t think we’re going to need 1500.

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So if we go back to a thousand, which was my target, basically. Let’s take a little bit more of a careful look at how much over travel there is.

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What we’ll do, we’ll set our zero here and we can compare over travel to there.

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So it’s about 10 millimetres onto that pattern. Vendor settings, what can we run X up to for acceleration?

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Maximum acceleration, 30,000. We’re already there.

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So let’s make that 50,000 shall we? Now, remember, that’s not what’s going to happen.

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That’s just now a new limit. Over to the user settings:X-acceleration 30.

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Let’s take it up to 40 shall we? Well, it didn’t fail. Let’s look at 50,000.

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There it is, 50,000. Now I’ve put a black mark on there, roughly where the over travel was at 30,000. We’re now at 50,000. You see,

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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we’ve reduced it by probably three, four millimetres. I don’t think we’ll push it any more than that.

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I think for an acceleration X of 50,000 and a speed of a thousand

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millimetres a second. I should be able to approximately check that with the scan speed on this machine, but just to be sure what we will do.

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100mm’s wide scan. Let me put the power up to something that shows, because remember at this high speed the exposure time hasit disappeared to almost zero.

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And let’s watch this baby run. Well, at the moment, I’m pretty well impressed with this little piece of kit.

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I’m just editing the video and as I said, I should be able to.

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I should be able to establish the speed that we’re drawing that line at. Well, we can see our scan lengths from here to here 100mm,

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which I set it, so that I could do just this sort of test.

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We can now step forward one frame at a time.

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And my frames are 50 frames a second, so that’s 20 milliseconds for every frame.

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And now, look, we can see that we’re just about on the beginning of the line.

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So one frame two three four five frames get me to the other end of the line.

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Five frames 100mm. And they’re 20 milliseconds per frame, so a 100 millimetres is taking.

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five of those, which is a hundred milliseconds equals 100 millimetres.

Transcript for K40 Laser Cutter Upgrades – Optimising Laser Machine Performance (Cont…)

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Now, it’s not going to take a rocket scientist to multiply that by 10.

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And that gets us up to a thousand milliseconds, which is one second.

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And if I multiply that by 10, I get up to a thousand

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millimetres. So there it is, a thousand millimetres a second, proven.

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I can sleep peacefully tonight. Okay, so you’ve seen a K40 running at a 1000 mm a second.

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It may be able to go faster a little bit, but I don’t need to, because I don’t have the exposure time with the power to use these sorts of speeds.

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It was just a challenge, a thousand millimeters a second.

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And I’ve met that challenge and I’m very happy. Now, just for a final direct comparison between what we had and what we’ve now got.

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450mm a second took 18 seconds before.

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Let’s just see what it now does with this new motor on. There’s our comparisons.

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What we had to start with, the very best that we could do is 200mm a second, with a high acceleration of 30,000 and we got down to eight seconds.

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But we can now push that down to five seconds because we’ve been able to push the acceleration up to 50,000 and the speed up to 450mm a second.

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Which is about as much as I probably ever want to use on this machine.

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So I’m extremely happy with the outcome of this project. Next time, we’ll start doing some real work with it We’ll do some cutting

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and we’ll do some engraving. We’ll see what this machine can really do.