Author Topic: Laser Beam Alignment  (Read 2881 times)

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #15 on: March 31, 2017, 01:48:54 PM »
Why not let the laser beam melt a hole in the plastic. Then spin the plastic 90 or 180 degrees and see if it just drills deeper or cuts at a different angle? Fasten a piece of card stock on the top of the plastic so you can realign the beam at the top. That should quickly tell you if there is a gross misalignment.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #16 on: March 31, 2017, 01:54:11 PM »
I suggest that the stepper motor could be held off the gantry and a Bowden cable used to move the head. The idea being that the mass of the stepper motor can be held in a non-moving location, maybe hung overhead. The Bowden cable (like a bicycle brake cable or a motorcycle throttle cable) can push or pull the Z-axis which should be sliding in a dovetail that has an adjustable gibb on one side to set it up correctly.
Bowden Cable: https://en.wikipedia.org/wiki/Bowden_cable
Dovetail slide: https://en.wikipedia.org/wiki/Linear-motion_bearing#Dovetail_slides

The slide could be made from one of those ball-bearing drawer slides to remove most friction. Or maybe one of these inexpensive slides:
 http://www.ebay.com/itm/160mm-HIWIN-AG15-CNC-Linear-Rail-Two-Bearing-Blocks-/321976629601
The Z-axis could be set up to be at the bottom of travel at rest and the Bowden cable used to pull it up into operating position via the stepper.

« Last Edit: March 31, 2017, 04:54:06 PM by mrehmus »
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

pedwards2932

  • Sr. Member
  • ****
  • Posts: 254
    • View Profile
Re: Laser Beam Alignment
« Reply #17 on: March 31, 2017, 04:23:59 PM »
The reason I was thinking a long acrylic rod is if you align with the top crosshair you would be able to see exactly where it hits on the bottom crosshair.  You could use lower power and it would probably work without burning anything.  The shaft alignment tool we used was a really low power laser and you could align it to the front and easily see where it hit on the opposite end.  If you had perfect alignment it was centered on both ends.  I am guessing this alignment would need to be checked periodically so this would be an easy way to do it.

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #18 on: March 31, 2017, 04:55:39 PM »
Maybe we should separate this thread into one on Z-axis motion and one on checking beam verticality.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2030
    • View Profile
Re: Laser Beam Alignment
« Reply #19 on: March 31, 2017, 06:25:14 PM »
@mrehmus - On a complete tangent, can you tell more about your Model Engine Builder magazine?
« Last Edit: March 31, 2017, 06:25:47 PM by ggallant571 »
SARCASM - Just one more service we offer here.

Koskee

  • Newbie
  • *
  • Posts: 43
    • View Profile
Re: Laser Beam Alignment
« Reply #20 on: April 02, 2017, 10:00:02 PM »
This is probably obvious, but careful with the acrylic fumes!

I was well aware of what was going to happen, but one thing I really wanted to engrave was acrylic because of its optical properties (for edge lit LED displays). So earlier tonight I figured I would just do a test run and see what I got for results. I cut a line no longer than about 10mm into a piece of 1/4" acrylic and the smell was really potent. Granted it still had the protective sheet on it, but it was definitely more than I had expected scent wise. Not sure if it would shine through without the protection or burn, but not something to be done indoors.

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #21 on: April 08, 2017, 11:28:23 AM »
I have come to the conclusion that the only way to do this with minimal software changes is to add a Z-Axis. Arguably a way to raise the frame of the laser is a better method mechanically but the software modifications to level everything would be significant and require another controller.

But the other midnight though I had was to make an height sensor for the system. They use them on CNC mills and they are not hard to build. There are other problems with such a setup but not insurmountable.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2030
    • View Profile
Re: Laser Beam Alignment
« Reply #22 on: April 08, 2017, 06:43:39 PM »
For operation I don't think it would require a change in software. All the z-axis motors (4 in my design) would be driven in parallel. The difficult part would be calibrating the initial height at the 4 corners. I envision putting an electric drill on the lead screws and individually setting each corner to the same height. Since the corners are relatively far apart I don't think this is a critical adjustment.  Only need one limit switch.
SARCASM - Just one more service we offer here.

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #23 on: April 08, 2017, 07:16:55 PM »
I have come to the conclusion that the only way to do this with minimal software changes is to add a Z-Axis. Arguably a way to raise the frame of the laser is a better method mechanically but the software modifications to level everything would be significant and require another controller.

But the other midnight though I had was to make an height sensor for the system. They use them on CNC mills and they are not hard to build. There are other problems with such a setup but not insurmountable.
How about something off the wall. Gelatin solidified in a tube might be burnable by the laser. Use clear gelatin and you could see the path.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #24 on: April 08, 2017, 07:25:54 PM »
For operation I don't think it would require a change in software. All the z-axis motors (4 in my design) would be driven in parallel. The difficult part would be calibrating the initial height at the 4 corners. I envision putting an electric drill on the lead screws and individually setting each corner to the same height. Since the corners are relatively far apart I don't think this is a critical adjustment.  Only need one limit switch.
I don't understand the drill 'bit'. Just turn the screws until they are even with a common reference point or a simple gauge and that sets zero. Better yet to put the limit switch on a swing-in arm that will stop the steppers when it makes contact with the work. Unfortunately, micro switches are not perfectly repeatable and may trigger somewhere in a 1-3 thousandths wide band. Easy to make an optical sensor for height zeroing though.

The problem I see is if one of the steppers misses a step and the bed then becomes uneven. However, if you put the height sensor on the carriage then you can move to all four corners and test for even height.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2030
    • View Profile
Re: Laser Beam Alignment
« Reply #25 on: April 08, 2017, 07:59:25 PM »
The z-axis depth on a mill is critical. On a laser it is a crap shot at best. Being off by a step would never be detected.
SARCASM - Just one more service we offer here.

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #26 on: April 08, 2017, 08:41:02 PM »
The z-axis depth on a mill is critical. On a laser it is a crap shot at best. Being off by a step would never be detected.
Except if you torque the frame, the laser doesn't make round circles. A step is very small but the lost steps could be cumulative. A height sensor wouldn't be hard to do.
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2030
    • View Profile
Re: Laser Beam Alignment
« Reply #27 on: April 09, 2017, 07:28:26 AM »
I have no problem adding sensors. My initial thought was to add a limit switch (HOME) on the z-axis. On startup the controller commands the steppers to trip and release the switches (X,Y,Z). That establishes a know position. Whether the switch is on the high or low (or both) side of the travel  is irrelevant.

Adding a distance sensor would accomplish the same effect from a different point of view.  Do you have any thoughts on specific sensors?

I have seen videos of CO2 laser cutters where the switch is not physically attached to the machine but rather temporally placed between the laser focus lens and the work surface. The z-axis is then jogged until the user sees the switch trip. Most of them seem to be constructed to give a known target distance, 50 mm for instance. I think I will make one.

Perhaps we could have a contest to build the most outlandish trip switch.
SARCASM - Just one more service we offer here.

mrehmus

  • Sr. Member
  • ****
  • Posts: 365
  • Pilot, submariner, model engineer, etc., etc.
    • View Profile
    • Model Engine Builder
Re: Laser Beam Alignment
« Reply #28 on: April 09, 2017, 09:13:29 PM »
For a height sensor, I prefer something that does not require much energy to actuate because some materials like leather or cloth are soft and the readings would not be accurate with a heavy probe or a sensor that required significant pressure for actuation.

I have a number of those U-shaped diode sensor/IR emitter sensors that are actuated by having an opaque piece of material interrupt the IR. If one made the probe arm of carbon fiber (printed or as a purchased rod) then the weight would be insignificant. They run on 5 volts so they are easy to adapt to a controller.

In the CNC mill world, height gages like this are swapped in and out with a tool changer. Some systems move a sensor in on a separate motion system.

In use, if one focused the laser, then moved the probe down until the gap in the sensor were blocked, then the system would 'learn' the zero point which would not change until the focus was again changed. Essentially it is a vertical limit or home switch.

Here is one sample of the sensor: http://www.ebay.com/itm/6Pcs-RAMPS-1-4-Optical-Endstop-Limit-Light-Control-Switch-3D-Printer-New-/282247383661?hash=item41b7414a6d:g:GRQAAOSwXeJYID-P
mrehmus
editor, Model Engine Builder magazine
Elekslaser A3 2.5 watt via Banggood
BCL
Qidi X-one 3D printer
Machine Shop with manual and CNC machines