Friday, 3 October 2014

axCut moves home, AFRo comes alive

axCut + Man Cave


It's been a long summer, but the man cave is now virtually complete and last weekend, the laser cutter (axCut) got moved into its long-term home:




AFRo


Whilst I've spent most of the sun-lit hours building, the dark hours have recently been spent on a new project - building an assistive feeding robot (named AFRo) for the UK charity REMAP.  The goal is not dissimilar to the HelloSpoon project (see Indiegogo campaign), but with enough differences to require a new solution.

You can are welcome to read through my detailed Design Notes as the design progresses, but for instant gratification, here is the latest video:


The hardware/software are both open source and published on github - see links in the Design Notes document, or search for the AFRo repo.    Hardware is fully modelled in OpenSCAD and predominantly 3D printable.   Total parts cost is currently around £260.

Comments/ideas welcome, but please read the Design Notes first in case they're already answered.


AFRo mk2

Although the mk1 mechanical design is functional and meets the design parameters, it suffers from too much vibration at the spoon tip :(  No good having a robot that shakes your food off the spoon.  It's not serious enough to abandon mk1, but it does mean I'm already working on mk2 in parallel.  It'll re-use most of the software, as the axis configuration is logically unchanged.  Here's the design sketch:


Will put up a more detailed post reviewing the design changes/reasons when I have time.


13 comments:

  1. Hey !

    I really like the axcut, nice project.
    I was wondering if you have taken a look at Smoothie for the electronics options : http://smoothieware.org/laser-cutter-guide
    It works very well, many people use it for their laser cutters, and we have native engraving in the works.
    You can email wolf.arthur@gmail.com if you have any question about it.

    Cheers.

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  2. Nice article as for me. It would be great to read something more concerning this theme. The only thing it would also be great to see on this blog is some pics of some gadgets. laser cutting machine

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  3. Hi Damian,

    Well done on the laser cutter build. It looks great. Thanks for sharing the design files on github too!

    Just wondering, with the 40W laser what is the fastest feedrate that you can use and still cut the paper reliably. I heard you mention in one of your videos on youtube that you were cutting slowly because it gave an excellent finish (looked in the ballpark of 1000mm/min). If you were only worried about cutting all the way through the paper and not concerned with the edge finish, how fast do you think you could cut the paper? 6m/min?

    Thanks! All the best,
    Tim

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  4. Hi Tim

    Thanks :)

    Excellent question, and would mostly depend on three things - thickness of the paper, focal length of lens (shorter better for paper) and how many little fiddly bits there are (i.e. can the cut rate get up to full speed and stay there)

    Assuming it was long straight cuts, I'd guess at 2-3 m/min, but I've never tested it to that extreme - mostly use it for cutting foamboard and/or fabrics. What do you have in mind?

    thanks
    D

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  5. Hi Damian,

    Thanks for the reply. I have a 5W diode laser from J Tech Photonics mounted on an X-Carve. I use it to cut paper piecing templates for a type of quilting (called English Paper Piecing). The paper I use is 105gsm recycled paper, that is quite brown in colour (like the stereotypical brown paper package). I can cut it at 800mm/min at full power, and it mostly cuts cleanly, with a few fibres remaining across some of the cuts. Focal length is about 40mm.

    At the moment I'm investigating building an instance of the AxCut, perhaps with a 100W laser tube, one of the important design goals being to cut paper pieces as fast as possible. My first assumption had been "20 times more power, should be able to go 20 times as fast", with the stepper motors probably topping out at 12m/min. Even 10m/min would be more than 10 times as fast as I'm cutting at the moment. However, reading the faq on the Mr Beam II Kickstart page (https://www.kickstarter.com/projects/mrbeam/mr-beam-ii-the-desktop-laser-cutter-and-engraver/description#project_faq_170095) prompted me to consider the absorption spectrum of the material and the wavelength of the laser. (I still reckon a 40W CO2 laser would cut through 4mm plywood at least 4 times faster than a 5W 450nm laser diode).

    Cheers,
    Tim

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    Replies
    1. Hi Tim

      Interesting, and that's some impressive cut speeds for a 5W diode laser. As to building a larger machine, high speeds are very dependent on a stiff/rigid frame, suitable drive system and minimising vibrations in the optics. The axCut design would need beefing up to run at those speeds, using decent linear rails (not v-wheels), more powerful steppers and stiffer frame elements at a minimum.

      I'd also recommend starting at 40W, then working up to 100W. These machines are tough to get working reliably and get anywhere near production level. They also need a lot of support equipment (fume extraction, pressurised air to the cutting head, water cooling). It's quite the learning curve!

      Happy to discuss further
      thanks
      D

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    2. Minimising vibrations in the optics is a good point. I hadn't considered that yet. Though, I was considering using a coreXY mechanism to minimise the amount of moving mass, so that would help.

      I've been happy with the NEMA23 stepper motors on my X-Carve. When I first built the machine I tested the maximum move speed, and it reached around 12m/min before it started to get high-speed stall. I had figured that the limiting factor was the stepper motor drive current, and that if I wanted something to go faster I would need more powerful stepper motor drivers (I'm using Pololu DRV8825 drivers which have 2.2A max phase current). That was with 1/8th stepping. I imagine it might go a smidgen faster with 1/4 or 1/2 micro-stepping.

      I'm an electrical engineer so I don't have heaps of experience with mechanical engineering. When you say 'decent linear rails' do mean something stronger than the v-slot rails like the buildlog laser 2.x design? The AxCut looks like it uses the openbuilds openrail linear rail. I guess mounted horizontally that would put a lot of pressure on 'internal v' wheels. I wonder if the 'external v' wheels used with v-slot have a larger contact patch.

      Considering beefing up the design, do you think only the X and Y rails would need to be stiffer (as long as the frame was mounted firmly)? I have seen 40x40 v-slot available for sale; perhaps that would make decent axis rails. Do you think any other parts of the frame would need strengthening/reinforcing?

      Thanks!
      Tim

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    3. Hi Tim
      yes - decent rails as in not v-wheels - something stiffer (less play) - I like the igus drylin stuff, but there are many other options.

      X+Y def stiffer, rest of frame will prob also need to be stiffer to resist flexing with the heavier/faster rails flying around.

      There are other things you can do with the frame design to stiffen it, but will reduce flexibility of the machine - e.g. reduce Z height, add a rigid link across the front of the machine, have structural panels that add shear resistance.

      thanks
      D

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  6. Wow!! i am very impressed with your lovely post.. i am so glad to left comment so interesting read, would love to read more here.... laser cutting machine price

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  7. Hi Damian!
    Small clarifying questions. All the mechanics running by managment of traditional Arduino + Ramps? Or something else?

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    Replies
    1. Hi Vasily
      Yep - Arduino + RAMPS 1.4 (with custom Marlin-based firmware)
      thanks
      D

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    2. Thanks for the answer. A little more clarification, if I may. Z-axis move 4 motors NEMA 17 uses two parallel turn like this (http://www.vicious1.com/assembly/wiring-the-steppers/) Driver 4988 or 8825?
      Thanks

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