08 – RF Laser Source Tests: Lets Understand What We Have

0:01now welcome to another session with my tangerine tiger please excuse the slightly echoey sound

0:07but i’m outside in my garden room at the moment it is um raining outside and uh yeah it’s not a

0:14very nice day but hey it’s a great day for doing what we’re going to have to do which is some theory and theorizing now we found out

0:22last time that we got what looks like the essence of a very nice machine but i need to understand this machine

0:27before i start playing with it and using it and so today is all about trying to

0:32decode how the machine works now i’m not going to go into the actual way in which the

0:40laser works because i haven’t fully decoded that yet but i’m getting there and sooner or

0:46later we will drill down and have a look at how the actual laser system itself works it isn’t

0:52terribly different to a gas tube laser but the way in which it’s controlled is different

0:59i haven’t got an SPT laser but good old SPT i love them dearly they really are a

1:05great company because they tell you a great deal about their product

1:10they’re not shy about giving you the truth and they have a version of it called the zamiya 30 watt which as

1:17you can see is exactly the same as the unit that i’ve got so i’m using their specification sheet i

1:24mean i spent a little bit of time looking at this sheet to try and understand what’s going on it says pump

1:30method rf excited i know what that means and i will explain that to you at a later date

1:35the rf frequency which is the thing that creates the ionized nitrogen as something called 100

1:41megahertz so we’ve got a frequency built into this unit which has

1:46nothing to do with the control frequency that’s a high frequency a radio frequency which is purely to get the

1:54ionized nitrogen in the tube version you would see that as the pink glow that’s the ionized

2:00nitrogen well that’s that would normally be generated by a high dc

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

2:06voltage as we know in the glass tubes well here it’s generated by high frequency as

2:13opposed to high voltage wavelength power average power

2:19interesting that word average we’ll come back to that later because i don’t fully understand that

2:24that basically to me means that the average output power of this unit is 30 watts

2:29which as we found out last time i thought i had a 30 watt unit but it seems to be delivering about 38 watts

2:37you can’t make up watts you could lose watts easily with a power meter but you can’t make them up so what we saw was real

2:45now it claims here that the output range is not to 30 watts

2:50how do we control that there’s only one input and that’s this pwm input here

2:58somewhere inside this pwm we are controlling the power and also the frequency

3:06of the machine because this machine works not only with radio frequency which is

3:13just a means of producing the laser action most of the time it’s working with a pulsing duty cycle

3:20not a continuous duty cycle so let’s try and understand

3:25what these terms here mean we’ve got rise and fall time duty cycle

3:32and modulation so those are the three terms that i’m going to be concentrating on today because i think

3:38i don’t know but i think they are the key features that are going to control this unit

3:44now eventually later on i’m going to be putting my oscilloscope onto the pwm terminal

3:51and trying to find out exactly what is going on so not only are we going to be trying to

3:56look at the electronics which are these features here

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

4:02because the electronics don’t actually tell you what’s going to be happening down on the

4:07surface of your material so there’s a relationship that we need to establish between the electronics and

4:14the real world first of all we have something called a pwm now we’ve we’ve set the pwm in the

4:20vendor settings to 25 kilohertz now from my previous work with the glass tube and the reader

4:26controller i know what the pwm signal looks like it’s basically a square wave

4:34okay now a square wave looks like this it starts high it goes low and then it

4:40goes back high again and then it’s joined onto another one and another one

4:46so we finish up with this square wave shape now this square wave here represents one

4:53cycle and we are talking about 25 000

4:59cycles a second and that’s what 25 kilohertz is so just to put some more detail on that

5:06so in one second if we divide one second by 25 000

5:12we finish up with zero zero zero four four zeros and a four now let’s

5:19just make some sense of that point zero zero zero comma zero zero zero

5:28so that’s a millisecond or a thousandth of a second and that’s a microsecond which is a

5:34millionth of a second okay and we have got one two three four three we’ve got four so here we are

5:4340. one two three four four naughts and a four so we’re talking

5:49about 40 micro seconds

5:55for a cycle so that’s as fast as the machine can actually pulse

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

6:02the problem that i had was when i sat down and looked at that and then i looked at another part

6:09of the specification which says pulse rise stroke fall time now to me

6:17that implies that when i’ve got a square wave

6:22i’ve got a square wave that does this

6:33where that time there the rise time and there the fall time

6:43is 100 micro 100 microseconds but hang on if that’s 100 microseconds

6:50and that’s 100 microseconds that means the pulse is going to be 200 microseconds long

6:57but i’ve only got a pulse that’s 40 microseconds long at 25 kilohertz so now i’m scratching my

7:04head and thinking do they mean microseconds or do they mean nanoseconds

7:09sometimes these values do get a bit scrambled up when it comes to

7:15specification sheets because the people that write the spec sheets don’t actually understand what they’re talking about

7:20so there’s conundrum number one we’re getting a mismatch of data

7:27let’s just assume that we put that problem aside for a minute and we just carry on

7:33and try and work out how do we control the power forget the actual frequency at the moment let’s just stay with

7:38the square wave it clearly says on here pwm duty cycle 0 to 100 what does that mean

7:47[Applause] well what that means is that whatever that height is

7:53of the square of the square wave means i’m going to get an output of 30 watts from the unit am i going to get 30 watts

8:00as i mentioned last time look we’ve got 50 percent of the time we’ve got 30 watts and the other 50

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

8:08of the time we’ve got zero watts so therefore the average of that is going to be 15

8:16watts now how do i get 30 watts out of this unit i think that this here

8:23[Music] will be expressed as 50 power [Music]

8:29on our controller because 50 percent of the time we’re getting

8:35power and 50 of the time we’re not getting power this is a slightly different way of

8:41using this term percent power in the previous glass tube situation

8:46the power represented current flow now it doesn’t represent current flow it

8:52represents the amount of time that the beam is on it’s on for 50

9:00of the time here and off for 50 of the time so if we want 30 watts out of this unit

9:07what we’ve got to do is we’ve got to ask the power to come on and stay on

9:14for 100 of the time and then go off and come back on again and go off and come back on again i mean

9:21it’s never going to go off technically i’m just drawing it like this to illustrate the point so here we’ve now got a pulse width

9:28modulation of 100 and that’s what we’re seeing here duty

9:35cycle 100 the cycle is 100 on and

9:400 off now equally well when we look at the average power that’s

9:46coming out of here it’s no longer 15 watts half the time it’s 100

9:5230 watts all the time so this is like 30 watts

9:57cw continuous wave so this is very much the same as a glass tube where we’ve got

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

10:04continuous output we’ve got no pulsing and that is how i think i did my testing

10:10because i set the power to a hundred percent so that’s why i’m seeing 30 watts okay now

10:19if i want to change my power in the same way that i’ve gone from 30 to 15 by using 50 percent

10:27and instead of going 50 percent we go say 10 percent on and all that time

10:35off 10 on off 10 on off so now

10:42we’ve got 10 percent of 30 watts so we’ve only got 3 watts now

10:53so here we are with 10 and we’ve got 10 of

11:0330 watts so we shall only have effectively an output of an average

11:10output of 3 watts so now hopefully you can begin to see how that by changing this

11:17ratio of the square wave how much it’s on and how much it’s off we can change the

11:23power output of the unit and that’s what this duty cycle is here not to 100

11:32we can change the pwm duty cycle and allow more power or less power we’ve got this big

11:38question mark here with the rise and fall time we now understand what the duty cycle

11:45means it’s a means by which we can control the power that outputs from the tube

11:52what about this other thing here modulation we set the vendor setting parameter to 25 000 cycles a second

11:59because we have chosen the rf tube within the vendor settings so when you

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

12:05look at the power controls now and press advanced you’ll see that in there you have got for each layer

12:11the opportunity to specify a different frequency

12:17so we can modulate as they call it the

12:22frequency between 0 and 25 kilohertz

12:28so what effect does that have here’s our standard 25 kilohertz that we’ve

12:34discussed already and we showed that if we reduced the power

12:39percent to 10 percent what we’ve done we’ve reduced the amount of time

12:46that element there as 10 percent of the cycle and in 10 of the cycle we’re going to

12:53finish up with three watts as opposed to a full cycle of 100 30 watts

13:02now when we halve the frequency to say 12.5 kilohertz

13:08we’ve got two of these cycles now we’ve reduced it to one cycle in the same

13:14period of time now when you look at this picture here you’ll see that

13:1910 of that longer cycle represents a much longer period of time

13:27so you might think to yourself yeah that means i’m going to get 6 watts

13:33of output it gets a little bit more complicated than that because that isn’t true

13:40we’ve still got 10 of this longer period of time so as well as this on period here being

13:48longer this off period here is much longer as well so the ratio

13:55is still ten percent so on average we should still get 3

14:01watts not 6 watts

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

14:08out of this pulse but however you look at it we’ve had that pulse on for longer than

14:14this pulse therefore we must be doing twice as much damage we’re doing twice as much damage but

14:21we’re taking longer to do that damage because the pulses are spaced further apart who said this was easy i

14:28have to point this out to you because we’ve got these two forms of control so we’ve got the mark space ratio

14:34control which as i said is our percent power

14:44and then we’ve also got this modulation control which has a different effect it slows

14:51down the pulses but it actually increases the amount of time

14:56that the pulse is on for in other words we’re likely to do more damage because we’re holding the

15:02pulse on longer now although the average power coming out of this

15:08is still at three watts we have still got

15:1630 watts available in every pulse

15:23and that’s the big difference between an rf pulsing system and a constant

15:30power system let me try and explain that in very simple terms that you can probably

15:38understand you’ve seen me before doing the candle test

15:44where i put my hand over a candle flame and i move it slowly across the flame it doesn’t hurt

15:52if i move it very very slowly it certainly does hurt all right the point that really is

15:59taking place there is we have got a fixed amount of energy coming from the candle flame

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

16:07we can share that energy across the surface of my hand depending on how

16:13fast i move my hand over the flame i could stop my hand and use all the

16:19flat all the energy into one spot [Music] or i can move my hand faster and i can

16:25share the energy out okay so i can make and this is the best

16:32way of imagining this the feel on your hand the faster you go the less it hurts

16:40well that wouldn’t be the case here because we’ve got 30 watts for every single

16:47pulse we’re not sharing the power out we might be sharing the distance out in

16:55other words this is a 30 watt pulse here and a 30 watt pulse here and a 30 watt pulse here

17:01i shall finish up burning 30 watt pulses across my hand

17:06right whereas with a constant system i will just generate a very thin

17:12line of energy across my hand so that’s the big difference between a

17:18constant on system and a pulsing system you won’t find this stuff explained anywhere else

17:25if you go to one of the big boys websites they don’t tell you how their machine

17:30works all they will do will give you menus which will allow you to select these numbers

17:36and you have no idea what they’re actually doing unless you have an understanding of the basic principles of

17:42what pwm is what duty cycle is and what and what the modulation of

17:48the signal is going to create so yes we’re still going to finish up

17:54with average 3 watts with this system but you’re going to finish up with the same powerful pulses that you are producing

18:02here as well 30 watts now with the glass tube laser

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

18:09there was a sort of emulation of this principle available to you in something

18:15called special mode and there the duty cycle wasn’t called duty cycle

18:22it was called this strange term for cooler so immediately you turn you turn special

18:29mode on you would get this 50 on 50 off you were no longer operating with continuous

18:36current but you could get back to continuous current by changing the cooler to

18:41100 okay and that just allowed this duty

18:46cycle to get longer and longer and longer so when we start using the machine we shall

18:54have to come back and look at this to try and understand what we’re doing when we’re damaging materials

19:01because i hope you can begin to see that changing the frequency has a different effect to

19:07changing the duty cycle so at the moment this is just speculation on my part

19:12based on the knowledge that i have so far i’m projecting what i will find and how this system works i don’t

19:20actually know but it will become completely clear when we start looking at the signals with the oscilloscope

19:28so we should easily be able to verify what’s going on here at a single pulse when we look at it on the oscilloscope

19:34i’m now going to show you how i think i’m going to be able to find out the relationship

19:40between what these signals are doing and what happens on our material here’s a surface and

19:47here’s my laser beam coming in like this remember what the curtains effect

19:52caused if we slow the beam down we burn deeper

20:00if we speed the beam up slow it down speed it up

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

20:07slow it down speed it up because we slow it down we’ve got more time to

20:13do damage and so we burn deeper now that’s what happens with a constant power

20:20b that is changing its speed slow down faster slow down faster slow down

20:28we will generate that sort of pattern now that makes the laser machine a very good

20:34velocity plotter and so what i propose to do here

20:40is do something like we’re allowed to do because it clearly says here that we can

20:46change the modulation to zero well i don’t want to go to zero

20:51but what i might do is to go down to something like 500 hertz if i run the machine

21:01at a thousand millimeters a second with a 500 hertz

21:09signal and 50 percent power i.e we’re going to finish up with

21:1650 on 50 off what sort of pattern am i going to be

21:22generating on the surface because on will produce a pit an off

21:28will produce nothing so i should theoretically be able to generate

21:37this sort of pattern on the surface now what sort of size pattern am i going to be expecting when

21:43i put these numbers into reality well look a thousand millimeters a second

21:50so in a thousandth of a second i’m going to travel one millimeter so what does 500 hertz equal

21:58so if i take one second and i divide it by 500

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

22:05i get 0 0 2 that’s 2 milliseconds

22:15so that means at 500 hertz i’m going to travel two millimeter

22:22two millimeters per cycle

22:31so that’s going to be very easy because technically what i should see is one millimeter one millimeter

22:41and one millimeter now whether 30 watts is enough to create sufficient damage

22:48for me to see is interesting in acrylic i’m hoping

22:53that i should be able to see some noticeable pits in addition to those noticeable pits if they are

23:02sufficiently clear i hope i might be able to examine them under the microscope and see

23:08things like this it may well look something more like that with curves but it should tell us

23:16clearly approximately what this rise and fall time is

23:22now whereas in a glass tube there is a relationship between the current flow and

23:30the power output the watts output so we had current flow which was pretty linear

23:35like this okay so these are watts and these are milliamps the milliamps go

23:40up at a steady rate and the watts do not go up at the proportional rate now here we’ve got a completely

23:47different situation i believe because we have got constant current and we’re switching

23:55that constant current on and off to get the change of average power because we’re chopping it

24:02up as i said we’re using the what they call the duty cycle to control the power

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

24:08so now i believe that what i’m going to get i’ve got no idea what the current is

24:13because it’s going to be constant and say like that but because we’ve got constant current i

24:21think that what we’re going to finish up with now is a graph that looks like this

24:26[Applause] 50 equals 50 percent of the available 30

24:33watts 100 equals 100 of the available 30 watts so therefore i’m anticipating a direct linear

24:41relationship between percent power

24:48and what and finally i think one of the very very first

24:53things we’ll do when we get back onto the machine [Music] let’s do a mode burn it’s a very nice

25:00six or seven millimeter beam and i’m expecting to get a nice

25:08sharp mode burn into a piece of acrylic how deep that goes will be interesting

25:16for 10 seconds because you’ve seen that i can bore my way through almost 25 millimeters

25:23in 10 seconds with a 70 watt constant power laser how far do i get

25:29through with a 30 watt laser i wonder you’re getting a front seat view of a mode burn

25:40now at the moment i haven’t got the air assist on this machine hooked up so i’m gonna have to use my

25:46my blower to um make sure i keep the fumes away from the front here

25:51otherwise they’ll catch fire not one two

25:57three four five six seven eight

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

26:03nine ten that’s not too bad so we’re very quickly

26:09swap the times two for the times three um beam expander and look at the

26:15difference north one two three four five

26:23six seven eight nine ten

26:31to be honest if i had a tube that looked like that i would throw it away because that mode

26:38burn is so blunt it’s pretty useless for cutting and for

26:46engraving so i think you can see clearly the difference in the power distribution between those two beams they’re the same

26:54beam one has been expanded three times and one has been expanded twice no competition i’m sticking with

27:01the two times at the moment because that has much greater damage capability now the other thing

27:07that’s slightly more difficult to see but when you look around the outside of

27:13that beam you can see all the low energy density power how it melted and bubbled up

27:21the acrylic and not evaporated it we’ve got a lot of low energy in the outer area of the beam

27:29whereas when we look at this one that damage around the outside is very

27:37minimal we’re concentrating a lot of the energy down the center part of the beam and

27:43that’s what i like to see what i’ve got here are two mode burns i’ve got one that i’m going to put

27:49behind the ones i’ve just done this one at the top here

27:55is for my 70 watt cloud ray tube this one here is from our times 2 rf

28:01beam and this one here somewhere times three rfb the point i really want to

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

28:08make here is that for a long time i’ve heard some

28:14now i don’t want to call it but effectively that’s what it is from the

28:21big boys who have always had a serious down on these cheap chinese glass tube

28:27machines that don’t last any time at all and i’ve been to exhibitions and i’ve heard those sorts of words mentioned

28:34but you cannot deny the facts now that i’ve got my hands on another type

28:40of machine which they claim to be the best in the world well look a 30 watt tube is a 30 watt

28:48tube you can’t perform miracles with 30 watts if you want to cut you need power

28:56so don’t regard these 30 watt rf tubes as cutting machines i never have

29:04and now i never will do yes they will cut but they will only cut what you could

29:10cut with a k-40 you might be able to cut three millimeter material you might be able to

29:16cut six millimeter material very very slowly but hey we should get

29:21on to that later but the fact is you require power to cut this is

29:26an axe this is a scalpel you cannot chop a tree down with a scalpel

29:32we move on from that interesting fact i’ve just carried a calibration on this machine but

29:40what i’ve had to do is to block this off with temporarily with a piece of card

29:46because the airflow at this end i was at risk of calling the doohickey

29:53down with this high airflow so i’ve had to protect it from the airflow to get say

30:00more accurate figures the figures are not quite what i expect

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

30:05so i’ll just go and plot them out and we’ll take a look at the graph okay please excuse the typo we’ll fix that

30:12later but it’s not important because hey the thing that’s important is my prediction of what this tube would do is

30:20um 80 wrong this is what i thought it might do it

30:27might produce a linear output yeah this is sort of linear but it’s not

30:34good enough to really be called linear i mean let’s be fair it’s probably about 30

30:40adrift so something is not quite happening as i

30:45expected and described to you previously at the moment i think this is a 25

30:50kilohertz signal and it’s operating with proportionate

30:56control and proportionate control should be as i described you earlier

31:02linear the fact that it’s not hmm

31:07there’s only one way to find out what’s going on and that’s to have a look at the pwm signal there’s my little oscilloscope

31:14that feeds into my laptop

31:20and gives us the opportunity to see what’s happening to the pwm signal

31:25what we’ve got here are zero volts and somewhere just about here we’ve got five volts

31:33okay so now i’ve got the system currently set to 50 percent power

31:39in other words i’m expecting to see half the peaks high and half the peaks

31:45low so let’s just check

31:50we’ve run a program and we can clearly see here we’ve got 50 high and 50 low

31:58so that’s working a treat the only problem is we’ve got two cycles

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

32:03per division and the divisions across the bottom there say they are 0.1

32:11milliseconds if we’ve got not 0.1 milliseconds for an interval that means one cycle is

32:18taking 0.05 of a millisecond so if i take one second

32:25and divide it by point zero zero zero which is a millisecond zero

32:33that one five so four naught zero five the answer comes out

32:40at 20 000

32:45hertz in other words 20 kilohertz

32:52now i thought i’d got this system set to 25 000 so we’re going to have to now go back

32:57and look into the vendor settings and find out what is it that is set to 20 000

33:04right we’re going to vendor settings read so so there’s my problem check glass 2

33:1225 kilohertz 1 and 99 we could set that to 100.

33:25right so i’ve hopefully got this set up now with 40 microseconds for

33:32two divisions in other words 20 microseconds per division now if you remember when we did the

33:37calculations for 25 kilohertz it was 40 microseconds per complete cycle so

33:43here we should see one division up and one division down

33:50there’s our 50 50 50 pwm it goes to the same level every time

33:59that that looks like about four and four and a half volts so we now change to 10

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

34:06so now we should see just a little bit high and the rest of it low like that

34:14so this is exactly as i described it to you this is the duty cycle 10 on 90 off and that 10

34:22there represents the 10 that you’re selecting on the keyboard if we select 99 we should see a little

34:29division let’s just resample again 99

34:35and there it is at just over four and a half volts so there’s no change in the signal level

34:40going to the rf unit the pwm is purely changing the duty cycle

34:46to change the amount of power that we’re putting into the pulse and we’re either putting

34:54long pulses or short pulses but they’re all the same power so on this machine it

35:00looks as though we cannot change the power by changing the level of the signal we can only change the

35:08power by the ratio of the signal length i’m just going to draw

35:15a circle put the padlock on and i’ll make that circle 10 millimeters diameter

35:23now 10 millimeters diameter means it’s got just over 30 millimeters of circumference we’ll put this

35:30into a cut layer we’ll make the speed about two millimeters a second then it will be 15 seconds roughly to

35:36run around the surface let’s set the power to 50 percent because we know what 50 looks

35:42like on the screen 50 50. we’re going to this advanced mode now the only one that’s available

35:48to us is number one and it says laser frequency well

35:54we’ll put that tick and this time we’ll change that to we had it to 25

35:59kilohertz before which took up two increments on the screen let’s take it down to 12.5 as we did

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

36:07with our example 12.5 kilohertz and then we should realize that it will take up

36:12four increments on the screen so now if i’m seeing this right

36:17we should see full signal level five volts and too high and too low and there we go

36:25just as predicted too high too low so really we’ve only got

36:32two controls for this machine we’ve got our power control which as i

36:39mentioned to you before changes the mark space ratio this is 50 power so it’s 50 high 50

36:46percent low if we change it to 10 power we get 10 percent high 90 low but there is a second function

36:54which is the modulation which is the frequency and that allows us to change the length of the pulse

37:02combined with a slow repetition rate so we can either have a fast repetition

37:08of a pulse at 25 kilohertz or we can have a much longer pulse getting closer to

37:16continuous mode long or short pulses at 25 kilohertz or long or short pulses or anything in

37:21between we’ve got control of the frequency we’ve got troll of the pulse width and that’s it

37:26here we are at the end of this session i think hang on let’s just turn this noise off

37:32oh my goodness me my ears are actually buzzing i’m gonna have to do a lot more than just a little bit of a cardboard

37:38deflector so in a strange sort of way there’s a lot less to understand on this

37:44machine than there was on the glass tube machine perhaps i’m saying that in hindsight now that i know a lot more

37:51about the glass tube machine but it seems as though this is going to be simpler

37:56so that’s actually converted it to grayscale already as it’s brought it in so let’s have a look to see whether or

38:03not we have the option oh yes we do we’ve still got our frequency control

Transcript for RF Laser Source Tests: Lets Understand What We Have (Cont…)

38:09now we’ve got our output direct which is greyscale so i can experiment

38:16with grayscale engraving on this machine because i’ve got a lot more control hopefully

38:21at the pixel level so we’ve got lots and lots of options that we can play with

38:26here for images we do some cutting i’m told that this system produces

38:32fantastic polished edges on acrylic am i cynical i think i was born with in

38:38my dna we shall have to see and find out just how good it is

38:43at what other people claim for this type of machine now we’ve got a machine that we understand and it’s working almost

38:50i’ve still got a few things to tidy up on this machine before we start working in earnest but hey we’re nearly

38:57there we understand all the tools that we’ve got to play with now which is great

39:03so thank you very much for your time and your patience and i shall see you in the next session