Lab robot conversion to laser cutter

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Re: Lab robot conversion to laser cutter

Postby macona » Fri Dec 31, 2010 9:10 pm

Did a little more work on the laser cutter. We are given the 24th to the 4th off so I have some time.

I picked up a Heidenhain IBV series interpolator for the encoder. The box that is comes in takes up way too much room so I popped out the board from the housing and am going to mount directly. The interpolator takes the analog sinusoidal quadrature output of the linear encoder and converts it to TTL quadrature. This will then provide feedback to the servo drive.

I laid out the boards today and mounted them and the servo drives as well. Now its time to start wiring. Whee...

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Laser cutter electronics by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Sun Jan 30, 2011 8:19 am

Finally got around to start wiring it up. After doing the servo re-retrofit on the Monarch 10EE I decided its time to ditch the old brushed glentek servos on the cnc mill and install some newer Mitsubishi AC Brushless servos on the mill. This should fix several issues I have had. Now I am waiting for boards for the conversion so I have nothing to do.

The servo connections for the encoders and stuff are a pain in the rear. the crimp on pins are a little over 3/16" long. Not designed to be hand crimped!

I too a set of the boards and set them up on the machine to ring things out to make sure I didn't screw up somewhere. I measured from ground to the ground on the x axis encoder, good, +24 to the encoder, good, same to the board arm, all good. Check continuity across gnd and +24, Uh-oh shows a dead short. After a bit of freaking out I found one of the flexible flat cables was loose in the connector and was pulled out at an angle shorting the two adjacent lines. Scared the crap out of me...

So most of the motor stuff is wired now. I still need to wire in the interpolator. But at this point I think I am ready to hook up the drives to power and start setting some of the parameters.

Image
IMGP6514 by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Tue Feb 08, 2011 1:18 am

I made some more progress this week. It was too darn cold in the garage to do any work so I got a friend to help me bring the gantry inside. Now it sits on my living room floor.

I got the bottom plate with the electronics bolted down and the power supplies mounted and wired in. Checked connections and everything seems to be OK. Eventually found two little issues. The stock board that the encoder on the X axis connects to and where the flex flat cables (FFC) terminate to before going to the arm had pins 26 to 30 on one of the two connectors ending in the board. This killed my 5v power to the gantry among other things. I jumped the connectors with some 32 ga wire and that fixed that. Second problem was the connection for the brushless motor on the Y axis. I got the pin order backwards. 1 was at 11 and 11 at 1. Luckily I was able to peel off the back spacer of the FFC and fold it over. I made up cables to connect the arm board to the carriage. I used those silicone wires I had posted about earlier. Pretty much the perfect length. I also made up a cable for the encoder, used some nice renishaw 12 conductor double insulated encoder cable that I picked up off ebay years ago.

I then made up a cable to connect the RJ45 serial connectors on the drives to the serial port on a laptop and installed the software for the drives. I managed to get the X axis tuned using the auto tune function, moves pretty quick with a resolution of .01mm per step. I dont have the encoder on the Y but managed to get it working in a low res mode where it reads the feedback from the motors hall encoder.

The Z axis motor was not so kind to me. Its a little maxon gear head motor. .18 amps at 45volts, 32 count encoder on the back, 24:1 gear box on it. First problem is the drive would not accept the single ended input from the stock encoder. Most drives have differential signaling built in and will take a single ended encoder input. Not these. I tried cheating and it almost worked but there was a whole lot of noise in the signal and it would not work right. So I needed to change the single ended input into a differential signal. Normally you would use a line driver but I didnt have one. What I did have was a mechanically bad encoder with line driver outputs. I took the board out and there was a line driver chip. I removed all the other components and took the bandsaw to the extra circuit board. I wired a connector to the inputs of the line driver IC and put a connector for the servo drive on the other end so the board is between the motor encoder and the servo drive. Finally the drive is happy.

Still problems though. Seems the motor draws less current than the drive really likes to see. This means the auto-tune is not happy. So I spent about 2 hours tuning the drive manually. Looks like this should work now.

Next up is trying to figure out how to mount the Y axis encoder scale and come up with a better mount for the Y servo motor. This one is just too floppy.

Here are a couple pics. One with the electronics mounted to the machine and the other with the machine guts exposed at night. I think I used too bright of LEDs!

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Laser cutter electronics by macona, on Flickr

5424068427_e9ce71fbb2_o.jpg
Laser Cutter at Night
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Re: Lab robot conversion to laser cutter

Postby macona » Mon Feb 14, 2011 6:32 am

I beefed up the Y motor mount. Silver soldered a piece of stainless to unitize. Much more rigid now.

I also got the Y axis linear encoder strip mounted down and machined an adapter to mount the reader head to the back of the carriage.

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IMGP6549 by macona, on Flickr

Once that was done I attempted to tun the Y axis motor. It just would not tune. Complaining about the encoder and all sorts of stuff. One time I tried to tune it I got a weird noise from the motor and that was all she wrote. Looks like I fried a winding. Swapped drives to make sure and got the same result. So it was time to redesign. I was thinking of various other drive methods like belts and stuff. I went to a friends surplus store and picked up a couple small DC servos. One was a MicroMo/Faulhaber 3863 series motor. Just so happens it has the same hole pattern as the old maxon flat motor. I had to mill out the shaft hole a bit but it seems to work. I also had to turn the shaft down to 3mm from 6mm to install the old pulley. I ended up using a 5C collet in the lathe to drive the motor while the motor housing was held in the steady rest. The shaft was hardened so I used a nice polished carbide insert to shave it down. Put a dab of loctite on the shaft and put the pulley in place.

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IMGP6540 by macona, on Flickr

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IMGP6542 by macona, on Flickr

I had left extra pads for a connection to a DC servo in case I couldnt get the brushless motor to work. I installed a connector on the board and wired up the motor. Ran the configure routine and auto tune and it tuned perfectly. Stinking powerful motor. Rated over 200 watts. I do need to machine a touch from the end support to clear the motor still. You can see the motor (black) in this shot:

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IMGP6547 by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Mon Feb 14, 2011 6:48 am

So now that the motors are tuned it was time to get this thing talking to a PC. That took some doing. First I made up a cable to connect to a DB-25 for the parallel port. Then it was software time. These drives are unlike any drive I have used before. They use programming environment similar to C to program the advanced features where they store the program on flash. It took hours of going through the documentation to gather all the commands I needed to make up a program that would set the drive to pulse and direction mode. Also with the encoder of the Y axis the interpolator multiplied the resolution time 2 so it gives me a 10 micron resolution, 2.5 micron in quadrature. Thats about .00009" per step which is crazy for an application like this. Luckily there the a pulse multiplier built in. Setting that to 4x it allowed me to match the X axis resolution of 10 microns in quadrature, around .0008". It also allowed me to kick the speed up on the Y axis. It will now do about 1000ipm.

Once I got the commands figured I got things going with an old 3ghz P4 I had lying around. Here is the machine running the roadrunner program that is in mach at about 400ipm. The X axis is quite a bit slower than the Y, much more massive and a weaker motor but it still does pretty good.



A few more pics:

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IMGP6534 by macona, on Flickr

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IMGP6539 by macona, on Flickr>

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IMGP6548 by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Tue Feb 22, 2011 8:23 am

Been spending the last week or so debugging things. X axis would just take off in the positive direction randomly. But only when commanded from the parallel port. If I send move commands in the control software via serial it moves how it should. Y axis would not hold position. If I move it falls short in the return to the original position.

It turned out both problems had a common theme... Noise.

X axis was getting noise in the step line when going in the positive direction. (Why positive only, I dont know) The noise was being picked up as step signals and the axis would take off until it tripped an internal overspeed limit. Luckily there is built in filtering. I adjusted it up to match the encoder filtering and everything started working as it should.

Y axis was a bit of a pain. First I had an issue with the multiplier. When I looked at the position status in the control software it was showing some odd position data, it was not multiplying right. Seems it does funny things when it is set in nvram and program code. Eliminated the multiplier in code and it moved pretty much as it should. Still it was not returning to the same spot after a move. If I rapid moved from 0 to 5 inches it would move further and then when I return back it would come up about 1/8" short. Weird thing was the slower I ran this test the more it would be off. Normally with an encoder you loose pulses and the motion is more than commanded. This was the opposite, it was receiving extra pulses while moving so it would come up short. I took my scope and put it on the lines from the pickup head to the interpolater board and found all sorts of noise. I disconnected the motor and a lot of it disappeared. I was getting all sorts of harmonics from the PWM from the motor drives. I tried using the built in filtering but it just wouldnt cut it. While the probe was connected I took a little ceramic .01 uf cap and put it from the signal line to the frame ground. That killed about 90% of the noise. I pulled the arm board off and soldered caps from each signal line to ground. I also solder in a couple 1uf caps near the connector to the encoder on the gantry board. That seemed to fix the problem, almost. It was moving the right distance in one direction but falling short in the other. I took the scope and put it on the TTL output of interpolator board. There was a strange glitch to ground in one channel and in only one direction. I then put the scope on the 1v p-p lines from the encoder. As I moved the axis one of the channels had a glitch where it would suddenly drop out for a few microseconds before resuming. I swapped out the reader head with a new one and that fixed the last remaining problem with the Y axis. It now moves exactly where it should, at least better than I can measure, or care to. 100 steps per mm, 2000steps per sec per sec acceleration, and will do over 1100ipm.

Now that I got that fixed I made up a plate to support the gantry board and guide the wires in the cable tray. Took some aluminum and milled it to the shape I wanted and mounted. I also yanked the hall effect cables from the cable bundle as they will not be needed.

Another thing I did was to stiffen up the Y axis. It was running on single truck on the small 10mm linear rail. The truck is preloaded but it is still lacking in stiffness. There is an auxiliary rail just below it with a couple more trucks. So I took some measurements and made a small plate to tie the two trucks together, I also milled away some of the part the truck mounted to to make up for the increased thickness. Tying these two together increased the stiffness substantially.

Now that it moves how it should I have found a problem that is causing me some problems. When the X axis moves the whole arm flexes. I have traced it down to the upright support that rises from the linear bearings. Much of it has been milled away for cable pass though and lightening. This has also made it pretty weak. Normally it would be fine because the original machine probably had S-curve acceleration and deceleration which helps a lot. Mach, EMC, and all the other cheap laser controls use a trapezoidal acceleration/deceleration curve that induces a lot of "jerk" into the machine which is very apparent in this set up. The far end wobbles back and forth like a leaf in the wind!

So, somehow I need to make things more rigid. So far I have two Ideas. One is to machine some plates to fill in the hollowed out areas on the X axis arm. Bolt through and probably epoxy them into place. Then Also make a heavy lid for the back side to box it in as well as I can. If that does not work Its on to plan 2. That is using a cable/belt and pulley system to drive the other side of the gantry. Another thing that might help is replacing the round rail guide system on the undriven side with some linear rails. That ought to give it a little more stiffness.

Now to a point where I need to get the laser and power supply. Also need to start scrounging up some mirrors. Its going to take more than I thought due to how I want to install the tube. Looks like I will need about 5 of them. Smaller than normal as well due to space constraints.

Here's a pic of the gantry board and support. The extra connectors are for things like home and limit switches.

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IMGP6555 by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Tue Mar 08, 2011 8:19 am

I ordered the laser tube and power supply combo from Cole Tech on ebay on Feb 24th, it shipped the 25th and DHL tried to deliver it the 28th. I got it on the 1st. Tube was intact. The only damage was to the power supply HV lead strain relief. A little glue will fix that. Did a quick rig up and did a couple short bursts and it looks like it is good to go.

I have decided to mount the tube and aiming laser to an aluminum base to build an optical rail of sorts. This will allow me to prealign the co2 and diode laser and drop the whole assembly in place when I am done. I will also mount two of the beam steering mirrors to the plate as well. Due to the design I am going to have to use 5 mirrors to the get beanm to the lens. Whee...

The rail is made from some 1/2" thick x 4" wide aluminum strip I had lying around. I still need to machine the tube mounts. There will be room for the red diode and beam combiner optics as well as room for a beam expander should the need arise.

I have also sorted out the cooling system for the most part. I have some small 18v stainless gear pumps from a Dialysis machine I took apart. Good flow and pressure. I also have a copper/stainless heat exchanger that was from the cooling loop on a LASIK machine. Combine that with a small reservoir and a flow switch that should complete things. Need to order a couple fittings as well.

The one thing that has kind of stumped me is getting rid of the rigidity issue I mentioned in the earlier posts. After looking at beefing up the riser support I have decided to abandon that idea. I put a indicator on the base near the linear guide trucks and measured movement down there when the beam was flexed. So I think even adding extra metal to strengthen the support will still leave me with a floppy axis. So I have decided to use two timing belts, one on each side of the X axis, attached to a common shaft. Hopefully this will tie in both sides together akin to a rack and pinion drive set up. I ordered the longest kevlar 5/16" MXL timing belts I could from SDP-SI and also two of the belt clamps. I will cut them to length with the clam attached to the gantry. One end of the machine will have bearing and pulleys on the common shaft and the other will have idler pulleys with tensioners. I have not decided what to use for the shaft. I want to keep the mass down but the stiffness up so it does not torque. I may use a piece of titanium rod I have had lying around.

Couple more pics from my iphone. First is of the cooling system parts, second is of the tube and power supply as well as the rail it will mount on.

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Laser cutter cooling system by macona, on Flickr

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Laser and power supply by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Sat Apr 23, 2011 1:02 am

I have not been doing much on the laser lately. I got the optics. Mirrors, beam combiner, and lens. I also made up the mount for the laser tube. I turned one end of the mount into a optical breadboard so I can easily mount my steering optics and combiner. We had a batch of stuff going to anodizing at work so I sent it out with it to be anodized. I mounted the tube to one room to give me more room in case I ever want to try building/buying a beam expander.

Next step is to get the combiner optics mounted as well as the laser diode and get them running coaxial with the laser tube.

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IMG_0153 by macona, on Flickr


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IMG_0152 by macona, on Flickr
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Re: Lab robot conversion to laser cutter

Postby macona » Fri Jun 03, 2011 7:13 am

Work has been busy. We have been doing 45 hours weeks and now for the next month we are on 50's. The movie we are working on, Paranorman, has been officially announced so a line has been drawn in the sand. You can see a little about it at:

http://www.laika.com

Stop-motion Zombies!

With that and other things, getting a new camera (Canon 60D), getting a new telescope, etc, my interest in the laser cutter has been derailed a bit.

So, I got the beam combiner installed with the laser diode. Set it up and got the red diode concentric with the CO2 beam. Also got the stock to reinforce the back support pieces and will also serve as bearing mounts for my stabilization idea.
Attachments
IMG_0460.jpg
CO2 laser beam combiner
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Re: Lab robot conversion to laser cutter

Postby tylerv » Fri Jun 03, 2011 2:22 pm

That's really cool that you're part of the team that made Coraline, that movie was really well done.

Where did you get the beam combiner gear? Are they just normal laser mirrors or are they semi-transparent or something?
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