DIY Laser levelling using webcam and laser level

[John McNamara]

Hi John,

"With a self levelling laser hitting a 2mm square target over the entire machine shouldn't be too hard assuming you have levelling feet on the machine, we all do this or better when we put up a shelf. This assumes we can weld the frame to within 2mm."

Assuming a vertical arrangement the only alignment required is to align the rough frame he two counter weighted wires. When a work piece is clamped in position it is also aligned to the wires.

The concept of using a "metrology frame" in this case for one axis is not new.
https://www.google.com/search?q=metr...5sCCs1M:&vet=1

It is important that the alignment wires are in line with the tip of the cutter at the point of cutting. This will greatly reduce any error caused by any angular misalignment of the z axis to the work piece. Abbes principal must always be honored.
https://www.google.com/search?rlz=1C...71.zasns7Fk5YU

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"Should also be noted that it is only the vga (640x480) web cams that have this small sensor area I think these are 1/6" diagonal sensors, other similarly priced but higher resolution cams have larger sensor areas. For example the raspberry pi camera (1/4") has a 4.6mm diagonal and another sensor I have the OV2640 has 4.5mm. It seems that the sensors are classified by the diagonal size of the sensor of which the active area with the pixels is smaller, this is why 1/4" > 4.6mm."

I think sarting with a low cost solution first then if necessary upgrading to a more expensive camera.

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"I like the idea of levelling a jig then grinding the surface as an alternative to shimming. What sort of grinder would you use for this?"

I had been reflecting on grinding but had substituted milling, strangely I should have written milling!
Grinders have a lot of inertia and take a long time to stop, they also make a lot of noise. A Small motor driven milling cutter ideally around 3mm can be fed relatively a lot slower and the motor can stop quickly. I suspect having a running spindle near the wire alignment system may cause the wires to vibrate. For high accuracy results it may be necessary to stop the spindle before each alignment cycle.

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I can imagine a jig short jig say 500mm that clamps around a piece of box section that can be micro adjusted for twist and level. I we bolted aluminium to the top of the box section you could probably skim it with a hand router with a small fly cutter in it. Skim the section under the jig then move the jig along, re-align it with the laser/wire then repeat. When you finish one rail then move the assembly to the other without moving the reference laser to bring the other rail into plane. Maybe a wood power planer could be used for the skimming, would be scary though.

The jig itself needs to be planar as you say but this should be straight forward on a milling machine.

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"What are you thinking for differentiating twist from height variation? I think with the laser two image sensors stuck out each side could detect twist same when you tram a mill with two dial indicators on a T bar in the spindle."

Two weighted wires suspended vertically will have no twist between the at all. These two wires are our meteorology frame. if we position our cutting stage relative to the wires using two cameras, make a peck cut then move X or Y,, check the cameras are still perfectly centered, make a new cut and so on our accuracy will be determined by the accuracy achieved by the camera system.

No system is without error however if you consider the above scenario the surface generated will have a surface that comprises a series of physical levels some high and some low. representing the accuracy of the measurement cameras and the positioning system.

Using a vertical alignment system, the exciting part is that the wires represent a plane that is far flatter than an inspection grade surface plate. The final result will be a surface that is extremely straight overall. With a surface similar to a scraped bearing surface.

Upon reflection I will make my test setup vertical.

As you may have guessed I have been thinking on this problem for a long time.

Cheers, Joe

Answers above.

[devmonkey]

Ok, I understand what you are talking about. The larger sensors are just as cheap btw.

This is what I'm going to do with the unit I've built.

[John McNamara]

It looks like the camera approach proposed by Devmonkey can solve two problems.

Generating an accurate plane surface with a Laser and camera as you have shown in his illustration
Or
Using stretched wire and camera's as a reference to machine a flat surface.

A great mind meld!

PS: I have located a scrap beam from a building site. I will have to weld up an adjustable base to keep it vertical. :)

Regards
John

[devmonkey]

I've tried to measure the cmos sensor under the microscope and it is roughly 2mm in the longest dimension (the one I'm using), will need to calibrate it with known shims to calculate um / pixel but using this rough measurement it is 2/640 = 0.003mm. The scale in the picture is 0.1mm per division.

[AndyUK]

I've tried to measure the cmos sensor under the microscope and it is roughly 2mm in the longest dimension (the one I'm using), will need to calibrate it with known shims to calculate um / pixel but using this rough measurement it is 2/640 = 0.003mm. The scale in the picture is 0.1mm per division.

Also important to note that as you're using a fitted profile you're able to give a measurement to a higher level of precision than that.

Que the mandatory accuracy vs precision debate...

Sent from my SM-G950F using Tapatalk

[Kitwn]

A little earlier I was tempted to ask, tongue somewhat in cheek, how, once the long ( X axis in my case) rails are aligned, we now extend these techniques to setting up the gantry. After a little more serious thought I came up with the following. The required equipment is satisfyingly simple and inexpensive. Sorry for a lack of drawings, I'm not at home among all my toys at present and I'm thinking and editing this as I write it. All comments and corrections gratefully received.
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Depending on your design, the same principles discussed earlier might be used to align the pairs of Y and Z axes rails when building the parts on the bench but we then need to square the gantry and tram the Z axis to bring everything together. Wanting to test for misalignment of rail pairs due to the stress of assembling the parts adds even more complication.
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I'm thinking that two taught wires (one in front of and one behind the gantry) stretched across the now perfectly aligned X rails could be used with a simple threaded sensor probe mounted in an offset bracket in the spindle in much the same way as a single dial gauge is commonly used for tramming but without the awkward setting up and possible errors of a glass plate sitting on the machine bed. For machines with the rails mounted on high sides this might not work. Design your next machine with your chosen alignment procedures already devised.
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One complication is that the wires must be perpendicular to the X rails and very close to the exact spacing required to give contact points with the probe arm parallel to the X axis or measured errors will be a compound of several possible alignment errors in the machine. By rotating the probe and adjusting it's height it is possible to use an ordinary multimeter to detect a setting where the probe just fails to make electrical contact with the wires at both front and back. If the spindle axis is not perpendicular to the X rails in the vertical plane these heights will not match. Unfortunately we can’t tell from these measurements if it’s the gantry feet that need shims or the spindle mounting.
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Testing at either end of the Y axis travel will check for any twist in the Y rails plane and variation of height above the X plane (I'm calling this 'Y axis tilt' ). At least we know where the shims go for these last two. All these errors will need to be corrected before moving on.
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I'm thinking of using a threaded probe rather than play with the software-driven Z axis height to do this as it's going to be quicker and easier.
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Your chosen gantry design means it may not be possible to position the axis of the spindle in the ideal position directly above one wire and check for two matching contact heights at two points either side of the spindle along the Y axis but any two points on one wire found by moving the sensor over as wide an arc as possible over a wire as close to the spindle as possible should work. Height differences measured here are only due to errors within the Z axis/spindle assembly alignment if there is no remaining Y axis tilt.
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Only after all this is done is it possible to skim the bed and then square the gantry by making the machine mark the corners of a rectangle on the bed and comparing the length of the diagonals.
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Kit

[devmonkey]

I've put the software up on github if anyone wants to play, I will add features as I need them or they are suggested here.

https://github.com/betzuka/laserlevel