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Wednesday, May 17, 2017

K40 Coolant Flow and Termperature Sensing

Background

The K40 laser needs coolant that is maintained at the correct temperature to prevent damage to the tube. It is not uncommon to forget to turn on a coolant pump or to have a pump or water system failure while running the K40. 
Sensors are easy to install in a converted K40 and the protection of the laser tuber certainly warrants the installation annoyance and cost of a flow sensor.

It is also desirable to know the temperature of the water and the tube. This post also outlines the installation of an inexpensive water temp sensor and control.

Donate

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Flow Sensor

Sensor

The loss of cooling water will certainly cause damage to the laser and the laser power system. Every system should have a flow sensor plumbed in series with the pump and the lasers cooling jacket.
The sensor that I use is:

This sensor needs to be installed on the output side of the laser. I made a hanger to hold it upright on the side of a 5 gal bucket. This way it insures that water is flowing out of the laser and it can detect any leaks from the pumps output to the sensors input.




Electrical connections;

The flow sensor is connected in series with the interlock circuit and in effect stops the laser from firing if there is no flow. 
See Build Schematics  for full machine details

If you for some reason do not want to add a sensor at least insure that the pump comes on with the machine. You can simply plug the pump and machine into the same power strip and turn them both on at the same time.

The End of My Tube Fell Off!

If you did not install a water sensor then at some point the pump will not be on, due to failure or  simply forgetting to turn it on, and the tube will overheat.

If the tube overheats the water jacket on the end of the tube can de-laminate and fall off.

Apparently if you are careful to keep it off the optical output area of the jacket you can use EPOXY it back on. I would surmise that high temp epoxy would be best.

https://plus.google.com/112581340387138156202/posts/Jz9gAKuSfTc

Temperature Monitoring

The laser must stay within its coolant operating range if it is to operate consistently and reliably. The cooler the laser is kept the more power it will be capable of. The power capacity of the laser will change with temperature therefore it is important to monitor the water temperature and prevent the laser from operating is the temp gets to high.
Install temperature monitoring electronics such as:

This device's relay contacts (NC) is also wired in series with the interlock circuit and will disable the laser from firing if the temperature is to high or low. The probe is put into the bucket near the output or the flow sensor.
See Build Schematics  for details.

This controller can be set up to produce an audible alarm outside of its set-points. (See the manual). I mounted it on thr front of the machine but plans are to move it up to the control panel later. The unit requires 12VDC so an additional supply is needed. Before I installed the 12V supply in my conversion I used a 12V brick plugged into a power strip. 


Enjoy and comment
Maker Don

K40 Coolant Pumps

Background

Information about common water pumps and coolant flow specifications

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Water Pumps

From +Scott Marshall :"When all is well, the stock system should fill a 1 gallon jug about 1/2 full in 60 seconds. About 1/2 gpm or 2 Lpm. .................. the Little Giant PE-1 is a good quality replacement pump which is just right for the k40 and available worldwide."


Enjoy and comment
Maker Don

K40 Lens Specifcations, Orientation & Cleaning

Background

Some links that pertain to K40 lenses

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Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.

K40 Laser Tube Specifications, Maintenance, Failure & Replacement

Background

A collection of information about laser tubes and their care.

Warning: run your laser with properly treated distilled water as a coolant.

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Laser tube operating conditions (Reci Laser):

  • Water cooling: using purified water; 2 to 5 liter/minute, (31GPH-80GPH)
  • Water temperature: 10-40℃, (50F - 104F)
  • The operating environment: temperature 2-40℃,(35.6F - 104F; humidity 10-60%.
  • The working current: test current is 29mA. Maximum working current is 29mA. The running current must be kept below 27mA. The life span can reach 8,000 hours if the current is kept below 25mA.
  • The ammeter must be connected to the negative electrode of laser tube.When it is working under over high current for long term, the negative pole will appear light yellow and the life span will be shortened rapidly.
  • To protect dust from going into the insulation sheath, please wrap it with plastic film.

Laser Tube Replacement

Tube Installation depends on the tube and there are multiple ways to connect to the pins on the tube. Pick your poison.

Basic Anode Connection Termination Methods

Unplug your laser from the mains power and let it sit for 1 hr.

Observe how the anode wire is connected to the tube including the wire routing and restraints.
Install the new anode wire in exactly the same way.

At the Anode end of the laser tube
  • Remove the silicon sheath from the anode connection. Minimize forces on the anode pin. It should pull off but if not you may have to cut it off.
  • Your anode wire may be twisted, screwed or soldered on the anode pin.
  • Remove or reterminaate the old anode wire. 
  • Replace the anode wire in the same way it was connected, twist, solder or screw.
    • If soldering use minimal heat. Some recommend using Teflon tape to hold wires that are twisted see video below.
  • Route and restrain the wire in the same way. Usually tie wraps around the tube moving away from the anode end toward the cathode end.
  • Flow silicon around the anode wire connection (use the white tube that came with your K40) 
  • Push the silicon tube over the wet silicon filling the tube. If you had to cut off the tube you will need to replace it with a peice of silicon tubing.
  • Add more silicon to the top of the silicon tube if needed
  • Let dry for 24hrs before using the machine
Alternate silicon: Permatex Blue RTV Gasket Maker. Available in auto and big box hardware stores.
703 adhesive silicone rubber insulation/potting/electronic waterproof sealant (the stuff that comes with the machine)

Other Methods

The videos below for removing a laser show connection and disconnection of the tube form its supply and can be used as reference example:
  • Videos
  • Replacement Tidbits from the web:
    • "Disconnect power from unit!!
      Gently pull the existing silicone tube off the terminal post by gently twisting and pulling it along the wire itself.

      Use a soldering gun to heat the existing terminal post to gently release the existing wire connections. Then cut and clean up those wires. Also clean out the silicone tube of the old residue. Of course you need to remove the water connections and drain the tube. When installing the new tube keep the same orientation as the old tube and reconnect the water lines. Before attaching the power leads, screw down the retaining brackets and make sure the grounding wire is secured properly.

      Since you are replacing a tube, you already have a tube and terminal posts to practice on first. Make sure the wire leads are stripped at least 1/2" long, enough to be hand wrapped tightly around the protruding terminal post. The advantage of Rosin Core Solder is that it contains a built in FLUX which helps to clean and bond.

      Before the wire strand is wrapped, make sure the silicone tube covering the wires is cleaned and placed back onto the wire. Once the wire strand is wrapped around the post, quickly heat and add some solder. Let it sit for a few seconds to cool and bond. The connection will be very secure. Just push the silicone tube back over the entire connection, completely fill the tube and connection with quick drying silicone and in about 3 hours once the silicone drys, you are back in business."

Arching [needs content]

Cleaning the laser tube water jacket

Replace all the water in reservoir with a couple of liters of vinegar and tap water... let it run for 12-24 hours replace all water with tap water only let it run for a bit... place outlet tube into a waste pan and flush adding a bit more tap water as your reservoir drains. Purge all water and replace with distilled water and some algaecide drops for aquariums. 
See: 

Laser Tube Specifications

Parallax: Laser Failure Modes and Warranty Info 



Enjoy and comment
Maker Don

Tuesday, May 9, 2017

K40 High Voltage Flyback Tests

Flybacks are Dangerous

OPENING AND EXPOSING THE INTERNALS OF THIS LASER POWER SUPPLY (LPS) IS DANGEROUS!

LIFE THREATENING VOLTAGES ARE PRESENT IN THE K40 HIGH VOLTAGE LASER POWER SUPPLY!

I do not recommend opening the LPS and trying to perform a repair. A typical LPS can cost only $70 -80 and a flyback is $20-30 the difference it not usually worth exposing yourself to these voltages and identifying a dead flyback is at best uncertain.

YOU PROCEED FROM HERE AT YOUR OWN RISK!

Other related posts are:

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Testing a K40 Laser Power Supply Flyback Transformer

A common failure item in a K40 is the flyback transformer in the LPS. This transformer is what converts line voltage to up to 20,000 VDC and when applied to the laser creates ionization. This flyback has a primary, and secondary. Although not yet verified we believe it has a HV diode and ballast resistor on the secondary. These transformers are potted so the internals are not exposed.
You cannot test the secondary circuit of these transformers without a tester. This test attempts to simulate the switching circuit on the primary as a meas of detecting an open secondary.

I am also working on a more definitive DIY flyback tester but this test can be done with household items so I thought I would throw it out there.

Donate your dead LPS and Flyback to a cause

I am using dead power supplies to test ways to diagnose and identify what is causing these supplies to fail. Please donate your dead LPS or Flyback to this cause and help the community get to a more reliable system.

If you want to donate leave a comment.... or get to me at +Don Kleinschnitz 

Testing Procedure

Note these instructions are for the flyback that has a 3 pin connector. I will update this post later for other types. The theory of the test is the same for them all.

Flybacks are difficult to test because the HV diode in the secondary has a high forward voltage. What this means is that to find out if the secondary is shorted a large voltage is needed. An ohm meter is of no use and will read an open. The primary can be tested with a DVM.

Step 1: Unplug the machine and wait 1/2 hr. 
Then with an insulated wire ground the anode of the laser tube. To ground the anode tape one end of a wooden dowel to a wire whose end it bare and connect the other end solidly to earth ground. Grip the insulating dowel with one hand and put the other behind your back gripping nothing. Touch the bare-wire end of the wire to the anode, an arc may occur. 

Step 2: Remove the LPS from the machine. 
This means that you will have to remove the large HV wire from the anode of the Laser. With all wires disconnected from the supply remove the cover of the LPS. If your Flyback has a plug connecting it to the PCB, unplug it. You can leave the Flyback mounted or dismount it to test it depending on the type of flyback. There are two general types of flyback one with a connector and one mounted directly to the PCB. The second type will require removal of the flyback from the PCB.
This post outlines flyback types: LPS Repair & Test

Step 3; Test The Primary
With an DVM set on a low ohms scale read the resistance across the black and yellow wires in the 3 pin connector. It should be nearly 0 ohms. If not ... donate it to me :)! its dead.

Step 4: Create a Spark Gap
Connect a wire to the red wire in the 3 pin connector. Tape the red HV lead to this wire. Do not electrically connect these wires together. Rather, create as small a gap as possible between these wires. This is our spark gap and will indicate if we can develop HV in the secondary.


Step 5: Wire up the primary
Connect one side of a 9V battery to the black wire in the 3 pin connector. Connect one end of a wire to the yellow pin on the 3 pin connector leave this end free.




Step 6: Test the Flyback
Rapidly touch the wire that is connected to the yellow pin on the 3 pin connector to the other terminal of the 9V battery. An arc should occur across the gap you created in step 4. If it does not ... donate it to me :)! its dead. If it does arc your flyback MAY or may not be good.


About the Flyback Test

The validity of this test has not been completely verified. Although this test should show if the secondary is inoperable it does not determine if the secondary can output the correct levels or quality of voltage. It also may not detect a shorted HV diode. If this test fails it is highly likely that the flyback is dead. If it does not fail it may mean that the flyback MAY be bad and MAY not :(.
To this point I do not have a bad flyback to verify this test with. If it works for you please leave a comment.

Enjoy and comment
Maker Don

Monday, April 10, 2017

K40 Laser Power Supply Driver Circuits

K40 Laser HV Power Driver 

As the investigation of the laser drive methods continues we now aspire to understand how HV power is applied to the K40 laser tube.
This post is a continuation of laser-power-supply-control-take-2.html, Whereas the focus in that post was the understanding and implemenation of digital controls, this post continues with a focus on understanding the internal driver circuitry of the LPS.

Other related posts are:


Contributors:

+Don Kleinschnitz

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematic

Warning

DON"T IGNORE THIS!

WARNING: LASERS AND THEIR HIGH VOLTAGE SUPPLIES ARE BOTH ELECTRICALLY LETHAL AND OPTICALLY DANGEROUS. THEY HAVE THE POTENTIAL TO KILL AND/OR BLIND YOU!

YOU ARE ENTERING A ZONE WHERE 20,000 Volts will be present!

  1. STAY FAR AWAY FROM THE HIGH VOLTAGE SUPPLY'S OUTPUT!
  2. WEAR PROTECTIVE EYE-WARE AT ALL TIMES WHEN OPERATING A K40!
  3. DO NOT OPERATE A K40 WITHOUT THE PROPER LASER INHIBITING INTERLOCKS INSTALLED AND OPERATING PROPERLY!
  4. USE THE CORRECT HIGH VOLTAGE SAFETY PROCEDURES

IN READING THIS POST YOU AGREE TO USE THIS INFORMATION AT YOUR OWN RISK!


I DO NOT RECOMMEND THAT YOU OPEN, PROBE, REPAIR OR OTHERWISE ACCESS THE INTERNALS OF A LASER POWER SUPPLY. YOU PROCEED FROM HERE AT YOUR OWN RISK!

Don't believe me? Here is an example of the LPS's energy!

Video by +David Cantrell


Safety

Most people are not skilled enough to be even near and certainly not inside a high voltage power supply such as this without special training and equipment. As an example this is the specially designed and built lab environment that I use to work on Laser Power Supplies. Nothing less is acceptable. 
Hopefully there is enough information on my blog to satiate your curiosity about your LPS or help you troubleshoot outside of the LPS's guts. 
The output of these supplies are a lethal 20,000 Volts but there are equally lethal voltages that can be found in the driver circuits (400 volts). This means that even if you disconnect the fly-back (where the highest voltage is created) lethal and high voltages are present in the voltage multiplier circuits.
These high voltages can also damage test equipment such as meters and oscilloscopes if grounding and input attenuation are not carefully planned.





LPS Scematics

The  updated schematic is used as the base for the theoretical theory of operation given below.
Note: this schematic is created from a G-G-G-G style LPS.

Embedded schematic below .....

PWM control

Much of the PWM's operation was covered in the related post so it is not repeated here.

HSwitch

The output of the PWM drives, with a complimentary signal, an Hswitch which in turn drives a transformer in a push-pull fashion. The secondary of this transformer drives the HV driver MOSFETs.

Charge/Voltage Doubler

The charge (voltage) that is dumped through the HV flyback is created using a doubler technique. Each of the doubler capacitors it charged respectively on each 1/2 cycle of the input AC through the full wave bridge. This results in 2x the input voltage on the series combination of the two capacitors.
This reference is what helped me decode this circuit: PowerSourcesForCW-Lasers

AC Line Voltage selection

There is a selection switch on these supplies for 115 and 240 volt operation. When the switch is in the 115 volt position only one of the capacitors is charged at time so the voltage across each is equal to the line voltage (115) and when in series they add to 2x line voltage (230).
When the switch is in the 230 volt position the capacitors are charged in series so each capacitor has 1/2 AC Volts or 115 volts each. The net result with 230 VAC in is the same as 115 VAC in. 

The operation is simplified in the image below.

Voltage Doubler Operation

HV Driver

The HV driver uses the complimentary signal from the Hswitch to dump the charge from the doubler capacitors through the flyback's primary. This results in a secondary high voltage that is roughly proportional to the flyback's winding ratio * primary voltage.

The image below is a simplified view of its operation. It shows that the current is dumped through the flyback in two directions, creating an AC like signal that has a period equal to the PWM.  I need to verify this theory with a scope.
Simplified Flyback Driver

Sense Transformer

In series with the flyback and in turn its current is a transformer that converts the flyback current to a proportional DC voltage. This voltage provides current (I) feedback to the PWM controller.

Open question: This method senses current in the flybacks primary but how does that know and regulate the current in the tube. The tube exhibits a negative resistance when it fires so how is the current in the tube measured and regulated, seems it isn't. 

Flyback Transformer

I am unsure at this time if the flyback module contains a ballast resistor and HV diode. I suspect that it does.

An example HV diode  specification.

Enjoy and comment
Maker Don

Sunday, April 9, 2017

Adding an Analog Milliamp Meter to a K40

Instructions for Adding an Analog Meter to a K40


Some vintages of K40's now have digital meters and pots. Some users find then sufficient and convenient others have found that having more information about the position of the pot and an analog representation of the laser tubes current to be advantageous.  

While you are adding this meter to your K40 you may also consider adding a high resolution pot and/or a pot position indicator: 
Thanks, to +Bob Buechler for testing out these instructions, doing the drawings and reporting on the results in this post.

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Installing the Analog Meter

Summary of the installation.

The analog meter is going to be installed in series with the wire that routes from the lasers cathode to the -L connection on the Laser Power Supply (LPS). 
[the -L connection is the leftmost pin on the leftmost connector on most LPS's]

Here is a simplified wiring drawing of the installation, courtesy of +Bob Buechler:
Before

Installation

You will need the following materials

  • New Meter Note: this meter is larger than used in the stock K40
  • Wire, as needed for your installation
  • Heat shrink tubing, as needed for your installation
  • Ring tongues, as needed for the meter you choose
  • Terminal Pin  and crimper

You will need the following tools:

  • Wire cutters
  • Soldering iron & or crimp-er to match the terminals you are using
  • Pliers or small wrench for tightening the meter nuts

Meter Mechanical Installation

  • Pick an appropriate place to install your meter, cut hole(s) as needed and install

Meter Wiring

  1. 1. Pre-check:
    1.  Verify that with the "Laser Switch" enabled, when you push the test function the laser fires.
    2. Power down and unplug the mains from your machine
  2. Find the wire that connects to the cathode (the end the laser light comes out of) end of the laser tube. Often its a black or green wire. 
  3. Trace that wire to its other end which should be connected to ground (L-) at the LPS. Note: never not ground the cathode or the (-) side of the meter directly to the frame. The lasers current must return to the LPS itself on pin -L. 
  4. Find the lasers ground port on the LPS. Its usually called L-, its the leftmost connection on the leftmost connector. Do not confuse this with the L that is on the rightmost connector with the DC voltages.
    L- on LPS with all green connectors

    L- on LPS with green and white connectors
  5. Remove the existing wire from L- and verify with an ohmmeter that that the LPS pin (L-) is connected to the FG pin on the LPS and that both of those pins (L- & FG) are connected to the frame of the machine. There should be close to 0 resistance to ground (frame) on these pins. Note: this is a good time to test that there is 0 ohms to GND at the frame pin on the mains connector.
  6. We want to reroute the existing wiring (that went from the tubes cathode to the LPS) to the (+) side of the meter. Do such by pulling the L- end of the wire that connects to LPS out of the harness enough to reroute it to the + side of the newly installed meters terminals. Note: Unless absolutely necessary do NOT disconnect the wire from the cathode as that is difficult to replace. When this step is finished the wire that previously was routed from the lasers cathode to the L- is now rerouted to the + side of the meter.
  7. Connect the wire of step #6 to the meters + terminal with an appropriate terminating terminal. Usually the meter has threaded studs with nuts and washers. I recommend using a ring tongue terminal soldered to the wire. See parts list above.
  8. It is common for the meters terminals not to be marked. If not marked start by connecting this wire to the left terminal of the meter (looking from the back), its a guess!
  9. Get a new piece of wire that is long enough to route back to the LPS (L-) pin from the (-) of the meter. 
    1. Use the same size or larger wire (yes it matters) and the same color if possible (colors do not matter but will be easier to trace later). 
    2. Connect this wire from the meters (-) terminal to the L- of the LPS.  
    3. Terminate the meter end with a ring tongue like step #7. For the LPS end use a crimped pin of the correct wire size. If you do not have the ability to crimp a pin at least strip back and tin the wire with solder. Insert the wire into the L- terminal and tighten securely.
  10. After insuring that you have not shorted anything with shards of wire etc prepare to return power to the machine. As a rule I vacuum my machine in the area I have been working with a crevice tool. Be careful not to create a static charge.
  11. Return power to the machine with your hand on the switch in case of smoke. No smoke? Then proceed.
  12. Turn the power adjustment pot (or digital control) to about 1/3 or less of its range. In case the meter is in backward we do not want to stress it. 
  13. To test the meter enable the laser [Laser Switch] and then push the [Laser Switch] while watching for movement in the meters needle. The meter should read the lasers current and you are done.
  14. If no movement is noticeable on the meter these things could be wrong:
    1. An error in the wiring, recheck using the steps above.
    2. The meter is in backward. Swap the wires on the back of the meter and return to step 10.
    3. The laser is not firing, check to see if the tube ionizes?
    4. If you cannot get it to work post a picture of all of the above connections and wiring with my G+ address +Don Kleinschnitz in the Laser Engraving 

Links on G+


"Ideally you want to cut the wire in a way that the meter can physically be placed in series with it leaving the cathode and the LPS end terminations alone. Just putting ring tongues where you cut it to connect the the meter. i.e The meter is placed in series with the current wire.

If the wire is not long enough cut the cathode wire long enough to reach the meter and put a ring tongue on it and connect it to + of the meter. Get another wire that is long enough to reach the LPS and put a ring tongue on it connected to the - side of the meter. Put a pin terminal on the LPS end.

Don't have a pin terminal and crimp-er? Alternatively tin the wire with a liberal amount of solder and insert and screw that into the LPS terminal.

If you want to keep the pin terminal you can splice it and a section of wire to a longer piece just insure you solder properly and cover it with shrink wrap."

Soldering Ring Tongues

I solder these type terminals because I have had problems with crimps corroding and/or vibrating loose. Theory is that if you crimp correctly this will not happen however soldering insures it does not.

Prepare the wire:

Strip the wire back far enough so that the bare end inserts fully into the barrel to its end

Heat-shrink:

Cut and slide over the wire a piece of heat-shrink that will cover the barrel of the terminal after soldering. The plastic cover may or may not come off or loose from heating. Most of the time I remove the plastic before starting.

Solder

Put the ring tongue on a heat restive surface or in a clamp. I lay mine flat on a piece of 600 grit sandpaper (the surface is heat resistant). Insert the wire through the barrel. Press with the iron on the ring tongue side of the terminal and heat while applying solder until the barrel of the terminal fills up. Depending on the size it may take a fair amount of heat. Don't put so much solder on it that it flows around the ring as that will impede attaching it to screws.

Finish

Clean flux from the terminal and slide the heat shrink up over the barrel and shrink it over the plastic if its still there. Sometimes the plastic falls off or needs to be cut off.

Some say this is overkill because its a pain to do but I have never had one fail over years of use.


Enjoy and comment!
Don


Monday, March 27, 2017

Measuring Laser Marking Quality

Background

There comes a time when you need to measure the output (markings) of your K40 with a known pattern in an accurate and repeatable way. This post focuses on tools to do just that. 

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Laser Marking Measurement Magnifier

This loop (not sure this one comes with the reticle) was acquired while I was developing laser printers. These magnifiers have optics and a removable reticle. The reticle in this loop allows you to measure lines spaces, line weights and spots.
Although this magnifier is nice because it has a reticle designed for measuring graphics art any magnifier with a graticule could be used and the phone table design adapted.

Some Other Magnifier Sources


  • https://www.tedpella.com/magnify_html/magnifier.htm
  • https://www.emsdiasum.com/microscopy/products/magnifier/measuring.aspx
  • https://www.edmundoptics.com/microscopy/magnifiers/handheld-magnifiers/peak-7x-or-10x-measuring-loupes/1782/

Phone Holder Table

I wondered if I could get good quality photos from my phone (S7active) laying on top of the magnifier which is below a fixed FL table.
Answer: Yes!.

I designed a simple table from acrylic that can be of course cut on your K40.


Table with LED light source (HF). Phone sits on top.


Measurements Photos



1 line on 2 lines off pattern. Measured output of laser printer

Marking Test Patterns

The most critical part of this tool is of course the pattern. The pattern was created in Inkscape as vectors. Vectors were drawn at the pixel level to create various resolution patterns in horizontal, vertical and diagonal directions. Line patterns with alternating line weights and spaces are used to test the systems response and the edges of these patterns when vector drawn and raster-ized can easily show errors. Some measurement values in mm are included on the pattern for reference.

Pattern labels:  the patterns are labeled with line and space values that indicate line and space values respectively [line&space]. Example: 1&2  = "one line width* ON and 2 line widths OFF. 
* Line Widths are relative to the images resolution in this case SVG resolution or 90.07dpi. Also note that the resolution of Inkscape can change as its version changes.

The .svg file is Resolution Test Pattern. I will keep it updated as I improve the patterns.

This file can be used in at least two ways and in any position(s) on the work-space:
  1. Download convert to Gcodes in your favorite CAM tool, I use LaserWeb. Then print this file on the test material subsequently measuring the image artifacts to insure that line width, position, spacing and edge acuity is correct. This tests vector marking.
  2. Save the .svg file as a .jpg and convert the image to a raster scan Gcodes in your favorite CAM tool, I use LaserWeb. Then print this file on the test material subsequently measuring the image artifacts to insure that line width, position, spacing and edge acuity is correct. This tests raster scan marking.


Picture courtesy of and marked by +Chris Menchion

Picture courtesy of and marked by +Chris Menchion

A micrometer will work accurately if you measure across multiple strokes.
Picture courtesy of and marked by +Chris Menchion

Diagnostics

This tool should be able to show errors caused by optics, electronics and mechanisms:

  • Errors in vector moves: "Positions, distance and start stop accuracy".
  • Raster scan synchronization from scan to scan: "Edge wiggling".
  • Resolution errors: "Lines not spaced properly"
  • Dot size adjustment errors: "Vector lines should create close to an even black fill if the spot size is correct"
The source of different errors can be isolated by comparing vector vs image marking of the same pattern. 
Example: vertical "wiggling" is noticed when marking. If there is no vertical "wiggling" on vector vertical strokes but there is on image vertical strokes this may indicate that there is a problem when the gantry reverses its horizontal motion. In the vector case the stroke is drawn vertically in one move. In the raster case the stroke is drawn by placing one dot under the other on each scan. When the gantry is scanning it marks a dot going right moves down a scan and then marks a dot going the other direction. Maybe a loose X stepper belt or its pulley?

Optimization

This tool should help in optimizing for materials!

Marking quality with a laser has inherently two challenges:
  • The power in a laser beam is Gaussian distributed with less power at its perimeter than in the middle. Therefore when two perfectly placed lines are marked parallel to each other the lower energy at the edge results in lower surface exposure and a banding effect** can be seen. This uneven power characteristic of lasers complicates the selection of beam size. Increasing the spot or power can reduce the uneven exposure due to overlay, but at the cost of resolution. 
    A Simplified Explanation of Exposure
  • From material to material exposure (how it burns) characteristics can vary widely. What darkly marks one material at a certain speed, spot size and power may not even mark another material at all. In the case of wood moisture content can even cause differences in the same wood type. 
** Banding can be caused from multiple types of errors in the system, including exposure, optical, electronic positioning and mechanical instabilities. 

This tool will help with optimization by making it easier to measure position, line weights, spot sizes while viewing their effect on the visual appearance of the pattern.

Enjoy and comment,
Don


Monday, March 6, 2017

Laser Response Charcteristics

Laser Response Characteristics

I moved the research that I have been doing into "laser response" to this post to capture it in a more focused way. 
Understanding the lasers response is an important part of getting to the best engraving control possible. The engraving control basics are described in Engraving-and-pwm-control.html. 
Understanding the relationship between the HV power (voltage and current), the tubes gas discharge characteristics and the lasing process of the C02 is integral to an understanding of how to optimize digital control of its power.

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Links to Related Posts

Electrical Modulation of a CO2 Laser

"Low frequency modulation can be achieved by pulsing or chopping the electrical power to the discharge. As the frequency is increased, the effect of the varying input decreases and above a few kHz, disappears entirely. The output of a DC or RF excited CO2 laser are both CW beams.
(From: David Toebaert (olx08152@online.be).)
This remark really holds for any kind of CO2 laser (the effect gets worse at higher pressure). It's just nature: it takes time for the molecules to 'meet' one another causing the delay. For a laser at 100 mbar (around 76 Torr) and a typical gas mix, the cut-off frequency is about 3 kHz. Above that the modulation of the input power is strongly damped and hardly visible anymore in the output power.

Simply think of the discharge as a *low pass filter for the input power, no matter how you excite the discharge. Of course, it's possible to modulate the input power at much higher frequencies (e.g. an RF supply can easily be modulated up to 100 kHz, that is, the Mhz signal is modulated at 100 kHz), but from the point of view of wanting to modulate output power, it makes no sense. Maybe it's beneficial for other reasons (e.g., discharge stability)."


*Whats a low pass filter?

The Effect of Modulation Cutoff Frequency 

The article above says that the laser cannot transfer input power changes that occur at a rate > than 3kHz. That means that the max time between changes that will be useful is: 3kHz  = 1/3000 = .00033 = 330 us. 
This means that in the model above the suggested pwm period (200us = 5kHz) is longer than the response time of the lasers gas ionization. 

If that is true then:
  1. The PWM period needs to be much longer or the gantry slowed down considerably
  2. The much faster times I measured (2us) by monitoring current suggests that it is not a  indication of the speed of light output. Is the current flow during ionization much faster than the light output?
More testing needed :(.


Laser Gas Discharge Characteristics

Negative Resistance
Negative resistance of a gas discharge: the voltage and current increase as described by ohms law until the discharge point. Then rapidly the voltage decreases and the current increases.

The hypothesis used in testing (above) and modelling; that the current flowing through the laser tube can be used as a faximile of the response of its light output does not track with the above modulation information :).

Laser Power Sources

Electric Discharge


Pumping the Laser


This video shows measurements of response speeds in the 4ms region.

Laser Operation

Lots of info here: 

CO2 Info Summarized From Links

Gas mixture & its function:
13.5% N2 :    excited by gas discharge (pink glow) collides with and moves CO2 to level 3
9.5%   CO2: molecule that lases at energy level 3-2.
77%    He:    collides with CO2 at level 2 and then collides with tube walls for cooling
2%      H2:    gas discharge disassociates CO2 into CO and 02. H2 mixes with CO & O2 to regenerate CO2  

Ionization Voltage: 25 KV
Voltage at lasing:    13-15 KV
Negative resistance: 200-300K

Breakdown voltages

https://en.wikipedia.org/wiki/Dielectric_gas
https://en.wikipedia.org/wiki/Dielectric_strength

CO2: Air *.95
Air:  3,000,000 V meter

Laser Tubes

Synrad 40 W Lasers: Specifies a 100us rise time.

References To Aricles and Previous Work

https://en.wikipedia.org/wiki/Grayscale
Understanding CO2 lasers
Principles of plasma discharge
Dynamic PSpice Model of C02 Laser Tube
Gas Laser Electronics
Basic Laser Principles


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Enjoy and leave comments and discussion;

Maker Don