Lab robot conversion to laser cutter

Post your build logs here

Re: Lab robot conversion to laser cutter

Postby macona » Sat Aug 04, 2012 5:52 am

The last few days have been major debugging. I got the machine back under computer control. When I did I found a bunch of issues. First the machine was moving pretty awful at low speeds in the X axis. Probably the tuning changed when I did my belt mod. Retuned that and it is pretty good. Next, the Z axis would just start vibrating randomly. I adjusted the aggressiveness of the tuning down and it seems to be happy now.

The biggest issue was the Y axis. The thing is like a tuning fork. Moving fast it was OK but going slow it would start resonating. The upwards portion of the Z axis also supports the Y axis encoder head. When the piece sticking up started vibrating it transferred down to the encoder head and made things go crazy. I noticed that is was all being supported by a rather thin piece of brass. I used the surface grinder to make a spacer that fit in the gap and glued it in place. This seems to support it and I am having a lot less issues but I was still not happy. Next I added another truck and a plate to tie them all together to the Y axis linear guides. This stiffened thing up quite a bit. I am pretty happy with it now.

I tried to etch something with the laser under power. A square. But it did not come out as a square. The X length as too short. I put a dial indicator on the axis and found it was not moving how far it was supposed to. It was not even returning to the same place. I used the servo software to issue a move command and it moved as it should, returning to the same place. So I was loosing step signals someplace. I pulled out my little scope and moved the axis and noticed the pulses were really short. Looked in the motor setting in mach and found the X axis was set at 0 milliseconds pulse length. Increased it and now it is happy. OOPS!

Next I tackled the limit switches for X and Y. X worked as it should. The signals from the Y axis would trigger a stop no matter where they were. Again with the scope. I found all sorts of noise going on in the lines. Looks like I was getting coupling from the motor power lines through the flat cables. I tried a small capacitor to filter it but it had little effect. Tried increasing the debounce and nothing there either. I finally ended up building a small circuit with a 74HCT14 schmitt trigger and a capacitor to filter out the noise. Works good, no noise now.

Still need to add a switch for the Z axis home.

Today a friend of mine came over and helped me get this thing around the house and back on it's stand in the garage. I went ahead and hooked everything and started to do some testing to figure out how to control the laser. While doing this I found my output power dropping. I looked at the diode temp and it was rising. The chillers could not keep up with the laser in the warm weather outside, about 85F. Not good. I had an old liquid to liquid heat exchanger I had pulled out of a dialysis machine a few years ago. I installed that in between the two chillers and then fed the other side of the heat exchanger from the output of and old Neslab RTE-5B recirculating bath chiller I have. That brought the temp down. Eventually I decided to try the neslab by itself after I saw the specs in the manual say it can cool up to a 400 watt heat load. It worked!

So I needed to modify the Neslab to be controlled by the laser power supply. Normally with one of these chillers they have a solenoid valve on the pressure refrigerant line that stops the flow when it reaches the desired temp. This chiller works a little differently. When it hits it's lower temp setpoint it turns on a heater which nullifies the cooling of the chiller. I added a SSR to the controls that allows the power supply to control the heater. Seems to work well. It does take some time to stabilize but when it does it is solid. Funny, this old chiller is 1/3rd the size of the fancy thermoelectric chillers and much, much quieter.

With my experiments on how to drive the laser I found another issue. I thought you could just set the frequency for the q-switch and use a TTL signal to drive it on and off. Nope. In external trigger mode you have to send it the frequency of the q-switch and control it that way. Kind of a pain. So my plan is to use a Teensy to make up a small frequency generator and drive the laser with that using something like an optoisolator to turn the signal on and off from the computer. The Teensy is overkill but it allows me to have a display for setting the frequency. The teensy is also a very stable pulse source too.

Couple pics. First is of the new plate to hold the third linear truck on the Y axis. Also you can see the spaces glued in place above it.

Image
IMG_2522 by macona, on Flickr

This is of the breakout board and the circuit I made to filter the limit switch signals.

Image
IMG_2520 by macona, on Flickr

Here it is, out of the front room and back on it's stand after something like a year and a half.

Image
IMG_2525 by macona, on Flickr
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby macona » Thu Aug 09, 2012 5:47 am

I tried the chiller on a hot day in the shop and found a problem. The chiller uses an 800 watt heater to regulate the temperature. When under the control of the laser power supply there is too much gain in it's PID loop and the temperature shoots way up before dropping and stabilizing after at least a half hour. Since there is no way to adjust the PID loop in the power supply I had to do something on the chiller side. Somehow I needed to reduce the power going into the water. Thought about a resistor but that would be a waste and just get things hot. Then I remembered I have a few of these guys lying around:

https://www.gavazzionline.com/pdf/RM1EAAdatasheet.pdf

They are a module in the same form factor as a standard SSR. The difference is instead of a signal in and on/off on the output these modules take a 4-20ma current loop and give you analog switching on the output side. I replaced the SSR with the module and installed a 5k pot with a 800 ohm series resistor to give me a 0-20ma current loop from the 24v signal from the power supply. This allows me to control the max power of the heater which stabilizes the loop much faster.

Then the start relay went out on the compressor. Lucky for me I had an extra lying around.

I decided to eliminate the cable tray that the Y axis cable lies in when it moves back and forth. It looked like it would cause trouble, especially when I add a hose for the gas assist. I had a piece of Kabel Schlepp cable chain the right size and made up a couple brackets to support that.

Next was getting the gas assist connected. I had a piece of tygon tubing the right length for the Y gantry through the cable chain. To get the gas to the X gantry I used a piece of thick 1/16" wall teflon tubing. I joined the two on the upper support by drilling and tapping a 10-32 hole though it and using Clippard fittings to connect the hoses on both side of the bulkhead. The teflon tube looped back along the back of the laser cutter and to a solenoid valve in the electronics bay and to a swedgelok 1/4" bulkhead fitting on the side. On the Z axis I drilled and tapped a blind 10-32 hole for another clippard fitting and used that to connect the tygon tubing to the coiled hose that will get gas to the nozzle.

I wanted something a little better than a generic power strip for the system. I had a old power distribution system out of a SGI computer system from some sort of semiconductor related piece of equipment. The unit has 10 plugs that are fed from a breaker box. The breaker box has an e-stop loop that trips the main breaker when the loop is broken or power is interrupted to the system. Ill tie this into a secondary estop that will allow me to kill the power quickly in the event of a power leak or something.

I still need to do something for the Z home switch and need to start finishing up the wiring.

Back of the chiller, know control max heater power and connector on right interfaces to the chiller.

Image
Chiller mods by macona, on Flickr

Chiller and power supply installed:

Image
laser cutter controls by macona, on Flickr

Cable chain installed on Y axis:

Image
Y axis cable chain by macona, on Flickr

Air line coming up from X axis bulkhead connection

Image
Y axis interface by macona, on Flickr

Z axis connection with gas assist hose:

Image
Z axis gas assist by macona, on Flickr

Gas assist solenoid:

Image
Assist gas solenoid by macona, on Flickr

Power distribution breaker box.

Image
Breaker Box, estop control by macona, on Flickr

Outlet strip:

Image
Power Distribition by macona, on Flickr
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby macona » Tue Aug 14, 2012 6:48 am

This thing is getting close to being finished. Last night I tackled controlling the laser from mach3. First I tried using the step pulse output to control the laser. I couldnt get a stable enough pulse train out of the computer for the laser to be happy. Next I tried a 555 timer and some optos. Didnt get very good wave shape out of it to make the laser happy. Finally I just used a 555 timer driven by the output signal of the breakout board to drive the laser trigger input directly. That seems to work. Took a little tweaking of the duty cycle and frequency but it looks like it will work for now. I plan on using a uC to handle the frequency generation so mach can control the power but that can wait.

I made the first cuts with it tonight. I used some 1/16" stainless as the sacrificial material. I used the roadrunner file included with Mach3 as the sample. I did a search and replace that replaced all the z-.1 with M3s and z.2 with M5s to turn the laser on and off. The scaling of the road runner files was set to .1, so the whole thing was about 7/8" wide. It ran all pretty slow due to all the tiny segments in the code.

Next I need to put the sides on an a bunch of other little things.

Attachments
IMG_2603 (1).jpg
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby macona » Wed Aug 15, 2012 1:21 am

I took some pics of the engravings i did last night after i went at them with a scotchbrite deburring wheel to remove all the burnt slag:

Image
Both engravings by macona, on Flickr

Image
Detail of small engraving by macona, on Flickr

Image
Detail of large engraving by macona, on Flickr
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby bdring » Wed Aug 15, 2012 1:43 am

That looks cool. Tell us more about the laser you are using.
Bart
"If you didn't build it, you will never own it."
bdring
Site Admin
 
Posts: 2966
Joined: Sun Nov 22, 2009 7:33 pm
Location: Chicago, IL, USA

Re: Lab robot conversion to laser cutter

Postby macona » Wed Aug 15, 2012 6:28 am

The laser is a Lightwave M210-HD-V06 Diode Pumped Solid State (DPSS) q-switched frequency tripled laser. The beam is 355nm, ultraviolet. 6 watts average power at 10khz rep rate, each pulse lasts about 30ns. Peak pulse power is probably in the 15 to 20kw range. These guys were around $60k new. They are used for micro machining, micro via drilling, SMD component trimming, wafer marking and cutting, glass cutting, and general marking.

One of the reasons these do so much more than a CO2 of ever 20x the power is because of the wavelength. First more metallic materials absorb this wavelength. Second is the spot size. at 355nm you can have a spot size 30 times smaller than a CO2 at the same focal length. Punch that into the beam calculator and you get some insane power densities.

Of course, all the optics are different. Mirrors are dielectric and lenses are fused silica or other UV friendly materials like MgF. And they are expensive, the lenses I have installed are almost $300 new from CVI.
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby macona » Thu Aug 16, 2012 7:23 am

Made some useful things with the laser cutter tonight. Some insulators for a circuit board out of Kapton.

Found my tuning was not quite stiff enough. I think that's fixed now.

macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Lab robot conversion to laser cutter

Postby macona » Fri Aug 24, 2012 4:52 am

I got 4 of the 5 sides on the machine now and installed a massive LED array for light on the top. I need to use my friends big CO2 to cut the front panel to fit.

A couple days ago I made the lens mount. I used a 40mm C mount extension for the body and made a spacer and flange to hold it all together.

Image
IMG_2668 by macona, on Flickr

Also the resonance came back on the Y axis so I added a bracket made from some of the left over stainless from the machine.

Image
IMG_2669 by macona, on Flickr

For the nozzle I decided to go with a factory made nozzle. I found some Bystronic nozzles on ebay, $100 for 12. 1.5mm hole. I had to order a 10mm x.5 tap which showed up today. I made the nozzle holder out of a piece of aluminum and single pointed the threads to fit the C mount. The air assist comes from the side to a quick disconnect.

Image
IMG_2674 by macona, on Flickr

Image
IMG_2673 by macona, on Flickr
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Hackaday!

Postby bdring » Fri Aug 31, 2012 10:43 pm

Bart
"If you didn't build it, you will never own it."
bdring
Site Admin
 
Posts: 2966
Joined: Sun Nov 22, 2009 7:33 pm
Location: Chicago, IL, USA

Re: Lab robot conversion to laser cutter

Postby macona » Sun Sep 16, 2012 8:04 am

Here is a video of the machine cutting out a shim for a canon camera out of .006 stainless. From what I read I can get a better finish by using nitrogen for an assist gas.

IMG_2783.jpg


macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

PreviousNext

Return to Build Logs

Who is online

Users browsing this forum: No registered users and 4 guests