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.
IMG_2522 by
macona, on Flickr
This is of the breakout board and the circuit I made to filter the limit switch signals.
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.
IMG_2525 by
macona, on Flickr