DIY Laser levelling using webcam and laser level

[devmonkey]

Hi Bert and everyone,

Here are some renderings of the laser-plano-meter I've been trying to describe.


It consists of a square device sat on 4 spherical feet at the corners. 3 corners of the square are rigidly connected to form a triangle (orange part) with laser attached. The forth corner is attached by the green arms to the triangle with flexures that allow it to pivot up and down with respect to the triangular plane, effectively the square is allowed to fold along its diagonal. The camera sensor is attached to the forth corner.


The laser will project a line on the sensor, the height of this line is related to the angle of the fold. The goal is to find the sensor reading where ALL 4 feet are in the same plane thereby providing a method of measuring the error of any surface from a plane. We will call this sensor reading ZERO.

To find ZERO we place the device on any surface, doesn't need to be a plane. We then take the laser height measurement H1 in this position. Now rotate the device 90 degrees about the Z axis and replace it on to the same surface so that each foot is in the same place as its predecessor was in the first position. Now measure laser height H2.

With both H1 and H2 we can calibrate the device. ZERO is the mid point between H1 and H2.

Now place the device on the surface to be measured, e.g. the pair of X rail beds of the CNC frame. The deviation from ZERO will tell you how much to adjust the frame under the 4th foot in order to bring the surface into plane.

An alternative way to think of it is if you just placed the non-zero'd device on the machine frame and take the laser height measurement, then rotate 90 degrees and repeat, if the heights are different you need to adjust the frame. Make the adjustment, rotate the device back to its original position and repeat until the height readings match.

EDIT
Should be noted that this device could be constructed with a DTI instead of a laser as per a normal repeat-o-meter. In this case you would have just the orange triangle and replace the laser with a long arm with the DTI on the end. The problem of course would be that the error due to the long arm flexing due to its own weight and the pressure from the DTI spring would far exceed the resolution of the DTI. This is not a problem with the laser beam as it wont bend no matter how long it is.

Cheers, Joe

[driftspin]

Hi Bert and everyone,

Here are some renderings of the laser-plano-meter I've been trying to describe.


It consists of a square device sat on 4 spherical feet at the corners. 3 corners of the square are rigidly connected to form a triangle (orange part) with laser attached. The forth corner is attached by the green arms to the triangle with flexures that allow it to pivot up and down with respect to the triangular plane, effectively the square is allowed to fold along its diagonal. The camera sensor is attached to the forth corner.


The laser will project a line on the sensor, the height of this line is related to the angle of the fold. The goal is to find the sensor reading where ALL 4 feet are in the same plane thereby providing a method of measuring the error of any surface from a plane. We will call this sensor reading ZERO.

To find ZERO we place the device on any surface, doesn't need to be a plane. We then take the laser height measurement H1 in this position. Now rotate the device 90 degrees about the Z axis and replace it on to the same surface so that each foot is in the same place as its predecessor was in the first position. Now measure laser height H2.

With both H1 and H2 we can calibrate the device. ZERO is the mid point between H1 and H2.

Now place the device on the surface to be measured, e.g. the pair of X rail beds of the CNC frame. The deviation from ZERO will tell you how much to adjust the frame under the 4th foot in order to bring the surface into plane.

An alternative way to think of it is if you just placed the non-zero'd device on the machine frame and take the laser height measurement, then rotate 90 degrees and repeat, if the heights are different you need to adjust the frame. Make the adjustment, rotate the device back to its original position and repeat until the height readings match.

EDIT
Should be noted that this device could be constructed with a DTI instead of a laser as per a normal repeat-o-meter. In this case you would have just the orange triangle and replace the laser with a long arm with the DTI on the end. The problem of course would be that the error due to the long arm flexing due to its own weight and the pressure from the DTI spring would far exceed the resolution of the DTI. This is not a problem with the laser beam as it wont bend no matter how long it is.

Cheers, Joe

Yes, that really helped.

This is a clever design.

I will try this later. I think a simple laserpointer will do i guess in this scenario.


Thnx Grtz Bert.



Verstuurd vanaf mijn SM-A320FL met Tapatalk

[devmonkey]

Afternoon all.

I've finally got back to my machine project. I gave up with trying to create a planar surface in one shot and as the weather had warmed up I poured epoxy, this looks like it has worked well and made a very close surface for final levelling using the laser and shimming if required.

Anyway the purpose of this post is to describe a new app I put together today for laying the master rail straight. I decided it would be easier to use a taut wire rather than the laser for this and a cheap USB microscope.

So armed with some 0.28mm black fishing line I found in the garage and a club hammer I tensioned a wire parallel to where the master rail will sit. I used some white insulation tape on the machine frame below the wire to provide good contrast for the software and the wire runs over a couple of bolts that run through angle iron supports clamped to the ends of the machine frame. The wire is anchored at one end and the club hammer suspended from the other, the fishing line stretches out quite a bit and you can see the nylon flowing under the microscope, I waited for it to stop flowing before doing anything else.

The microscope is attached to a hiwin carriage and the new app accurately locates the wire allowing you to zero the tool then reports the error as you slide the carriage back and forth. A 3D printed clamp allows the microscope to the rigidly attached to the magnetic base.

Nothing new in the process that other people have performed other than the app that lets you achieve excellent accuracy with little effort. The resolution is roughly 3um per pixel repeatable down to less than 1um (relative to the straightness of the taut wire obviously).

The wire locating algo is quite different from the laser gausian model and seems extremely robust. For those interested it locates the two edges of the wire using a median gradient threshold down each column of pixels, regresses lines down these edges and auto tunes the threshold until it has exactly two lines that completely cross the image from left->right. It then bisects the two edge lines to locate the wire centre. This removes any error from tapering of the wire due to stretching under tension. You hit zero then the app will will show you the relative error to this point as you move the rail and/or carriage about.

Anyway I captured this video showing the app working on the machine frame:


I will use this tool to set the master rail over the next day or so.

Cheers, Joe

[Michael Gilligan]

Afternoon all.

[...]

Anyway the purpose of this post is to describe a new app I put together today for laying the master rail straight. I decided it would be easier to use a taut wire rather than the laser for this and a cheap USB microscope.
[...]

The microscope is attached to a hiwin carriage and the new app accurately locates the wire allowing you to zero the tool then reports the error as you slide the carriage back and forth.
[...]

Nothing new in the process that other people have performed other than the app that lets you achieve excellent accuracy with little effort.
[...]

The wire locating algo is quite different from the laser gausian model and seems extremely robust.
[...]

Cheers, Joe

.

With apologies for absence ... it's been a while since I was here :

That sounds like a great development, Joe
I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

MichaelG.
.

Edit: Just off to grab that code

[devmonkey]

.

With apologies for absence ... it's been a while since I was here :

That sounds like a great development, Joe
I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

MichaelG.
.

Edit: Just off to grab that code

Hi Michael,

I actually wrote a different app for the taut wire method, I don't think I uploaded it anywhere. It has been a while but I think it made use of the wire not crossing the sensor exactly parallel to the pixel rows to gain excellent sub-pixel resolution and it also took a bisector of the line edges as the line shadow is not gaussian when lit from above by a microscope. This also takes care of the converging or diverging wire edges which you can see under high magnification and are caused by the wire stretching more in the centre of the span than at the edges as it flows.

Unfortunately I wont have access to the machine with the code on for a few weeks. Thanks for the offer of some wire but I don't really need it, I found that black fishing line worked perfectly since the app is tolerant of an imperfect wire as described above.

Edit:
Actually it turns out I did upload the code, fill ya boots!
https://github.com/betzuka/laserleve...uilds/wire.zip

Cheers, Joe

[Kitwn]

Gret stuff Joe!
Having just found out how effective taut wires can be for machine alignment I can really appreciate the value of the new software. Do fishing shops sell stainless steel leader in the UK? It's what I used and may be more stable than nylon.

One measurement I was completely unable to make on my machine was the straightness of the fixed rails. That may have now changed. I just need to work out a carriage arrangement for the round supported rails.

Kit

[devmonkey]

Gret stuff Joe!
Having just found out how effective taut wires can be for machine alignment I can really appreciate the value of the new software. Do fishing shops sell stainless steel leader in the UK? It's what I used and may be more stable than nylon.

One measurement I was completely unable to make on my machine was the straightness of the fixed rails. That may have now changed. I just need to work out a carriage arrangement for the round supported rails.

Kit

Hi Kit,

Yes they do sell steel leader, music wire is also an option. These axis are only 1300mm long so normal lightweight fishing line seems to be perfect, very uniform and black meaning it is easy to resolve in the software. It only flows for around 30s after tension is applied and under the microscope you can see when it stops. The length I put on the machine yesterday hasn't stretched at all over night.

Some things I noticed that maybe useful:
1. The microscope (£20) must be focused once at the beginning and then not touched. Turning the focus winder shifts the optical axis which would throw off any measurement. The focus winder is solid enough not to move on its own.
2. The microscope cable must be tied to the carriage to avoid any force being applied to the back of the scope pushing it off axis.
3. M6 bolts make perfect wire guides for 0.28mm wire, the wire locks into the V of the thread.

The depth of field (variation in objective distance where object remains in focus) of the microscope is probably <1mm so you need to get the wire guides to the same height so the wire is not sloped, I set mine level with the top of the epoxy bed using a ruler. The wire is then suspended a few mm outside the epoxy bed.

If there is enough interest I will share the app, needs a bit of a cleanup first as it was a quick hack.

Cheers, Joe

[Kitwn]

Joe,
I think it would be well worth sharing the app. I know Johm McNamara shared a lot of very useful info regarding the use of electrical sensing of a wire during the earlier pages of this thread. I was inspired by his work to do my tramming with taut wires alignment a couple of weeks ago which proved very sucessful. But the simplicity and low cost of your solution (who hasn't got a laptop these days?) makes it accessible to everyone. I will have to think about how to make the most use of it AFTER I've spent the next couple of weeks tarting my house up to make it more saleable but I suspect another round of alignment could be on the cards in the future thanks to your efforts.

Fitting shims is cheap and easy. Working out WHERE to fit the shims is the trick!

Keep up the good work!

Kit

[John McNamara]

Hi Joe

You just made my day.

Gee using a microscope with your software is a huge step, 3 um = 0.00011811 about a ten thousandth of an inch imperial. accuracy.

Using wire or fishing line allows the measured line to be accurately positioned. By anchoring each end of the wire to the machine frame precisely you can place the linear rail exactly where you want it. A lot easier than pointing a laser from one end. It also allows you to easily place two rails parallel to each other, by simply measuring the space between the ends.

I would really like to try your new software. In fact I am quite excited.
While tweaking it You mentioned that you used black fishing line piano wire is bright and I guess would require a dark background instead of the light background you used to enhance the contrast of the line you used in your experiments.
Maybe the ability to invert the pixel colour in the contrast discrimination code would be a useful addition.

Wire or mono filament fishing line? I can think of a number of applications where the the measuring system will need to be left in place for days or weeks when say a large machine installation or While a DIY machine is being built, All plastics will keep creeping and possibly break. Music wire will retain its elasticity indefinitely if it is not loaded above its elastic limit. I use Roslau music wire with great success. Size 0 is .009 Inches in diameter. I never reuse it (From the coil it is perfectly straight you do not want any kinks) a small coil will last for years of hobby use.

There is another use for this system! A non contact plumb line sensing system or maybe even a pair of plumb lines!!
Two suspended plumb lines will always remain parallel and perfectly vertical in relation to each other (Ignoring the curvature of the earth that is only measurable at great distances.)

The two wires define the edges of a rectangular flat plane that in this case is measurable to .0001 inches using wire and your software. I am going to think some more on this....... I have an idea.

Regards
John

[devmonkey]

Hi John,

I've put up the first version of the wire app here:
https://github.com/betzuka/laserleve...uilds/wire.zip

Extract and run wire.bat, needs java installed as per the laser app. The wire needs to be crossing the rectangular field of view of the sensor in the short dimension, e.g. if your sensor is 640 wide by 480 tall wire should be crossing the sensor from top to bottom.

It doesn't care whether it is looking at a bright wire on a dark background or vice versa, just needs a decent contrast and the microscope focused so that the wire edges appear reasonably crisp. My fishing line is just black mono filament, super cheap kids stuff that I already had. The main reason for the different algo from the laser is that the objective is lit from the front rather than behind, so it isn't acting like a shadow camera, this means you get lots of reflection off of the surface of the wire which would misslead anything searching for a gaussian, or indeed searching for anything other than the wire edges.

Your idea of using it to check for planar surfaces is brilliant ! I could stand my machine on end, drop two plumb lines and measure the relative error between the two lines from each respective rail.

At some point I will integrate it into the laser app so all the other error plotting stuff works. Do you have a microscope to test it with? If not this is the one I'm using, it is also very handy for SMD soldering etc.
https://www.amazon.co.uk/Microscope-.../dp/B07BF86SRP

Cheers, Joe