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  1. #31
    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.

    Click image for larger version. 

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    Last edited by devmonkey; 4 Weeks Ago at 04:52 PM.

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  3. #32
    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
    Last edited by John McNamara; 4 Weeks Ago at 02:26 AM. Reason: Typos!

  4. #33
    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.

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  5. #34
    Quote Originally Posted by devmonkey View Post
    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.

    Click image for larger version. 

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    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

  6. #35
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 5 Hours Ago Has been a member for 1-2 years. Has a total post count of 114. Received thanks 20 times, giving thanks to others 2 times.
    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.
    -
    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.
    -
    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.
    -
    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.
    -
    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.
    -
    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.
    -
    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.
    -
    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.
    -
    Kit
    Last edited by Kitwn; 4 Weeks Ago at 09:03 AM.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  7. #36
    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

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  9. #37
    Kitwn, about using it for tramming I would attach my sensor block to a T-bar in the spindle as if I was tramming a mill with a single dial indicator. Rotate the spindle and take sensor height readings at 0, 120 and 240 degrees rotation. Take plane described by these 3 3D points, calculate the plane normal and determine the error to the plane normal of your x axis plane, then shim the z axis until the normals are the same.

    I will have a think about squaring but this is usually easy to do with dual x axis machines after skimming the bed by drilling 4 corners of a large square and checking diagonals using a stick with an indicator on the end, adjust home proximity sensors, re-home, repeat.

    If at any point after initially bringing the x rails into plane you need to re-establish this plane in order to do something like tramming, it is unlikely the laser can be put back where it was initially. However since the rails are still planar the laser can be setup again and 3 points measured 2 from one rail, one from the other and the x plane normal established relative to the new laser normal. This is similar to moving between machine and workpiece coordinate systems in a CAM programme. For tramming we would align the spindle normal to the x plane normal via the laser normal, i.e. When the two errors are the same the spindle is trammed.
    Last edited by devmonkey; 4 Weeks Ago at 09:41 PM.

  10. #38
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 5 Hours Ago Has been a member for 1-2 years. Has a total post count of 114. Received thanks 20 times, giving thanks to others 2 times.
    I'm very interested to look at your software on github. I'm no great programmer but have an unused Raspeberry Pi and a Pi camera which my brother -in-law sent me. I've been trying to work out what to do with them so this might be a possibility.This is exactly the sort of application he'd enjoy seeing it used for. It would be a large sensor block though with the Pi included as the camera attaches directly to it.
    -
    Part of my concern with working out an exact series of measurements is separating the possible sources of a given error and being able to align the machine in a systematic way. There's no point making the axis of the spindle exactly vertical until after you've ensured the axis along which the Z assembly moves is vertical and that can't be done until the Y rails and gantry mountings are set up and so on.
    -
    Some assumptions might be possible if your mechanical construction is very accurate but my machine is built using welded steel construction, a drill press and hand tools without access to a milling machine or other precision machining, so it's accuracy will only ever depend on being able to make measurements and correct errors with shims. I designed the whole thing with that requirement in mind but it's being able to make accurate measurements without spending more on a variety of gauges than on the machine itself that has made this thread so interesting. Like many hobbyists I have more spare time than spare money and there's great satisfaction in following Arthur Wellesley's maxim.
    -
    Kit
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  11. #39
    Hi Devmonkey

    I downloaded and set up the camera software from Github.
    setting up is quite a process, a mate who is a far better programmer than me led me through the environment variables setup. I am not used to this sort of programming environment.
    Once installed correctly the software compiled without an issue.

    I was only using the webcam on my laptop and a hand held laser line (not point) generator. It worked very well.

    A logitech webcam was also tried it worked but there were strange fresnel like circles produced with the laser. The logitech camera had a quite large lens. The laptop camera did not display the same aberrations. its camera is tiny.

    I also tried a fuzzy pencil line drawn on paper that worked OK too.
    A piece of wire should be no problem.

    Over the weekend when I have time I will set up a test on a granite surface plate with some precision gauges. and a proper camera with and without a lens on a stand.

    It will be very interesting to get a better idea of repeatable accuracy. I am sure it will be very good.

    Congratulations Joe, great job.

    Regards
    John

    PS:
    I have started to draw up the flat surface generator I described,
    I want to make it 90% from Laser cut 5mm steel plate. Using a single universal beam as the main frame (100ub 23) I know that that profile is available in Australia and the UK Hopefully Europe and the US too. It will hold an up to 100x100mm RHS Workpiece. To be used as linear rail support beams for routers and mills.
    I hope it works! There is only one way to find out.

  12. #40
    Quote Originally Posted by John McNamara View Post
    Hi Devmonkey

    A logitech webcam was also tried it worked but there were strange fresnel like circles produced with the laser. The logitech camera had a quite large lens. The laptop camera did not display the same aberrations. its camera is tiny.

    I also tried a fuzzy pencil line drawn on paper that worked OK too.
    A piece of wire should be no problem.
    If you are using a laser with the (crap) optics of a webcam then you will get all sorts of weird patterns and probably more problematic non-linearity meaning each pixel will register slightly different height errors, best to get an old or cheap webcam and rip the sensor out and bin the optics. If you want to stick with optics then use a piece of white paper as a screen between the laser and the camera, focus the camera on the screen.

    With the pencil line did the gaussian detection work? I would be surprised if it did as the pencil line would be lower intensity than the paper. I would need to invert the intensity I would think for this to work properly with a pencil line or wire. Also to use as a shadow camera you will need to flood the background with an even light source, maybe a white led behind a piece of diffusion perspex (the translucent white stuff). This is to eliminate false triggering from the otherwise random background intensity of your workshop wherever the camera is pointing.
    Last edited by devmonkey; 4 Weeks Ago at 03:49 PM.

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