Eclipze's SMD Pick'n'Place Build....

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    Default Eclipze's SMD Pick'n'Place Build....

    I've played around with quite a few designs for a small hobby desktop pick and place machine in the last 2 years. But I've finally come down to a solution I'm going to build :-) It's actually the 20th design model

    There is of course many different approaches you can take. I've held a core theme for my design... small capacity desktop machine, light weight, support a flexible design for modifications and support fast movements.

    It's not a design for full blown production, rather a design suitable for prototyping or a short pre-production run. I specifically want it to support placement for components with footprint around the size of 0805, SOT23 and fine pitch IC like TSSOPs. The option for two placement heads has also been of interest. This is either for two different pickup nozzles, or to have one setup for paste dispension. I tend to machine my own stencils for small runs anyway, so the paste head mechanism hasn't quite been finished yet.

    Ultimately... this will never been anything like having a proper production machine. It's far more of a hobby... some people build ships in a bottle, others are happy to spend many late night procrastinating over a feather weight pick and place machine hahaa.....

    I am concentrating on the basics. Not the end goal. Vision based alignment, auto head changing, automatic feeders are all future upgrades. If I spent too much time looking into all the extras, I'd never actually get the first model up and running. So please bare that in mind with any comments.


    Basic design specs...
    X Axis Travel is ~160mm
    Y Axis Travel is ~440mm
    Z Axis Travel is ~25mm
    X & Y step resolution is 0.0125mm
    C Axis step resolution is 0.14 degrees
    PCB area is flexible, currently shown as 220x180mm

    I really wanted the design to have a lightweight head, to enable fast acceleration and also to keep the cost down. I've looked at many approaches using double rails and ballscrews, which always add a significant amount of weight and cost. However the more I played with the idea of light weight, the more I realised I could achieve a rigid design with just 3 linear bearings, belt driven. I have the igus Drylin T Series rails for X, Y an Z, and 2.5mm pitch, 6mm wide belts.

    The X and Y are using NEMA 17 motors, and the C is using a tiny 20x20x32mm stepper. All are bipolar 1.8 degree step. The Z axis are all controlled by RC servo motors. I sure a lot of people are going to choke on that one hahahaa.... I have picked servo motors for good reasons. They are light, very fast, inexpensive (consumable) and easy to drive with the electronics (no stepper drivers). They have a radial movement, which means their translated linear movement has variable precision. The way I have the mechanism set, I achieve the highest precision as the placement tip descends close to the board. In addition, if the tip over travels (tries to crush the part underneath), it can't. The only downward force the tip has is the weight of the carriage/head. Once touching the component, only this weight will be on the component, after which the servo bearing disengages from the mating surface. I'm hoping that although I may not have fantastic precision, I can safetly overdrive the placement without risk of any damage.

    The head has a separate tape indexing pin to feed the tape with. Each strip of tape also has a square box where the component is picked up, so component alignment by bumping can be done at the point of pickup. Rather than traversing to a specific cavity to perform the function.

    The C-Axis uses a rotary tube fitting, which is held in place by a large bearing. A gear is attached to the rotary tube fitting, whereby the stepper can rotate the bottom half of the tube fitting (which is connected to the pickup needle). The top isn't fixed, however the air tube will restrict it's movement anyway.

    I'm using ribbon cable for passing all data/power. All the actuators are so small, that the power requirements are relatively low. I still use 16 wires for the Y Axis stepper (4 wires for each stepper wire) just to be sure. I really like the idea of using ribbon cable, as it tracks so nicely without any sort of guiding mechanism. It's so very light too. It should impeded movement like a track conduit system would, and it much lighter than having an overhead cable bundle.

    I have an adjustable camera on the head, so placement can be watched via PC. Expanding to vision based feedback is something for future work.

    I have tried to create a flexible mechanical design solution. The use of angle aluminium is the basis to achieve this. If something isn't performing as I'd like, or an upgrade is desired, it's likely that only a bracket needs to be changed or modified. I have used 7.6mm polycarb where where thicker material is needed. The baseboard and the component feeder bases will be made out of corrian. It's a nice hard/stiff material that machines well, and should be nice and rigid for this application. I'm just using freebie off cuts. The frame is inch square aluminium with plastic joints. This leads to future possibilities for what is mounted underneath.

    Design Variations
    The base board defines the basic layout, which I currently show with placement area in the middle and tape strip feeders on each side. Those tape strip feeders are 8mm tapes, 16 per side. But these can be variations of other tape widths and component trays. I hope to have standard trays with most used component values, then others to cater for more specific needs. If I have a short run to place, I should have enough feeders that I can double up on components that are used more, or swap trays in/out as needed. I've also got the idea to mount reels underneath... if it's worth going to that effort of course. Including upward facing vision for component alignment is quite possible... it's just a variation of the base board to provide the real estate to mount it.


    I've spent a lot of time considering many different options. Input is welcome, however at this stage of the game I'm reluctant to make any significant modifications in order to get to first base - something that does the basics. I'm mostly into construction/build mode, modifying the design to suit build/machining requirement. Please keep in mind how small this machine is and it's intent. Aiming for design elegance, not design overkill :-)

    I'II be machining the parts over the next couple of weeks, and will post some pictures as I go. Hope everyone finds it of interest!

    Similar Threads:
    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_01-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_02-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_03-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_04-jpg  

    Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_05-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_06-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_07-jpg   Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_08-jpg  



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    Here's the first part done... the stepper to pulley coupler.

    I milled a flat spot on the 10-tooth pulley, which mates with the coupler. It's a tight press fit, and also has a set screw for good measure. The stepper shaft also has a perpendicular pin going through it, so I have a tight slot in bottom of the coupler to mate with this pin.

    There was no way I could mount this 10 tooth coupler on the 5mm stepper shaft... there wouldn't be enough metal left after machining the hole hahaa... I initially was going to have the pulley on it's own axle and bearings, then a coupler to the stepper - as you normally see. However I decided to make best use of the steppers bearings and to design a coupler to mate on the outside circumference of the pulley for a rigid solution. This was a far smaller footprint and less mechanically complex solution. Time will tell if the solution has a low enough deflection, or even if a minor angle offset with the stepper mount will suffice.

    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-stepper_coupler_01-jpg   Eclipze's SMD Pick'n'Place Build....-stepper_coupler_02-jpg   Eclipze's SMD Pick'n'Place Build....-stepper_coupler_03-jpg  


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    Hey Eclipze-

    This looks really nice. The use of RC servos on the Z-axis is rather clever. Just keep in mind that they tend to drift over time and with temperature swings. Also the lifespan is rather limited on the cheap ones because of random gear failures and encoder wear.

    Can your design accommodate for Nema 23 motor on the Y-axis in case if Nema 17 does not cut it? Just looking at the clearance under X-axis and I think that the belt may rub there.

    Also, beware of the static electricity that may develop on the plastic parts rubbing against plastic. Like those clear covers on the feeder guides. If that is made of polycarbonate or acrylic, try to get the ESD dissipative variety if you can.

    Another observation. I think it may work just fine but I still feel uneasy about those unshielded flat cables carrying stepper voltages. The RC servos may not like the interference and the solution may be to put the stepper drivers right next to the motors. Since you are looking to use small steppers, you can find or build some really tiny driver circuits like this one here: http://www.pololu.com/catalog/product/1201. It can handle 2A and 24VDC just fine and will be able to drive Nema23 no problem.

    Regards,
    Kyryl



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    The X axis for me is the long axis. I assume you're looking at the belt clearance on the Y axis. It only has 2.2mm as it goes over the brown camera bracket support, which is less than I'd like. I look at machining a slot on that bracket to extend the clearance.

    The potentiometers in the servos do tend to wear out, which I'm aware of. You pay for what you get with these things. I've got some cheap GWS servos to start with, which after they die I'II replace with a good quality set. I plan to have an adjustment control via the software to control the servo offset, something that can be adjusted on the fly.

    I already have a Gecko G540 for this project, which is a 4 axis 10 step stepper controller. I need 10 bit to get the resolution I was aiming for, while relying on their mid band resonance control to get fast/smooth acceleration rapids. I'II run them at a high enough voltage to get good torque at higher speeds. I could fit a NEMA 23 for the X axis by pocketing it lower in the base board. I've actually already bought it too, a 185oz/in suited to fast RPM apps. It seemed such a big motor for the application that I was worried about it being strong it might cause damage if I hit the limits (even though I have limit switches). Picture below shows the size comparison. The NEMA 23 is on standby.

    The ribbon cable may not be good enough without shielding. It's definitely a low cost and very low movement resistance, which is why I'm keen to see if it could work. But if necessary, I have the room to put tracks in to take normal cables. Otherwise, I may need to do some filtering for the servos or try to use some thin flexible metal to adhere to the cable.

    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_09-jpg  


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    Quote Originally Posted by Eclipze View Post
    The X axis for me is the long axis.
    I thought it's your Y that is longer from reading your first message. Never mind, I was referring to the clearance of the belt driving the long axis but didn't think about the possibility of sinking the motor down. I'd definitely go with 23'th frame on the long one.

    Quote Originally Posted by Eclipze View Post
    The ribbon cable may not be good enough without shielding.
    Yes, look for adhesive copper foil on ebay or elsewhere. Make sure it's copper and not aluminum or nickel - you'll have to solder it to the ground. But before you do foil, see if a simple isolation of the servo conductors with ground conductors will work. Another sensitive circuit would be your video feed from the camera. It will pick up EMI like crazy unless well shielded.

    Let me know if you have troubles locating the vacuum ejector assembly. I have several collecting dust here.



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    I could always use the NEMA 23 and set a lower current limit... so in future I can easily up the power for more speed. Would also mean I'd have margin to tighten the carriage bearing for better lower tolerance (at the cost of friction). I'II have a look at the design tonight

    The vacuum ejector assemblies I've seen online look rather BIG. Appreciate the offer though! I'm probably more keen to see how well the mechanism I've designed will work hahaa...

    Copper adhesive foil definitely does sound an attractive solution. I hadn't decided yet if the air tube and USB camera cable would run alongside the ribbon cable, or if the video feed would also use the ribbon cable. I'm going to wait until the table is moving so I can get a better feel for how the ribbon cable and/or other cables will move before committing to an option.


    For now... the Y-Axis pulley brackets are done. Bearings are a nice press fit. I could do a better job of them a second time around, however the pulley is aligned perpendicular to the rail and should do the job nicely

    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-y_axis_belt_pulley-jpg  


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    The X-Axis platform and stepper motor mount is done

    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-x_axis_platform_01-jpg   Eclipze's SMD Pick'n'Place Build....-x_axis_platform_02-jpg  


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    Default outstanding!

    Dear Eclipze:

    Fascinating project - you must be a master machinist, with a very well equipped shop-
    quite out of my league, but I'll follow your progress closely, as there will be a lot to learn...

    About the linear guides you're using: I believe they're the ones in this catalog:

    http://www.igus.com/pdf/drylint.pdf

    right? There are 4 different sizes (15, 20, 25 & 30mm) as well as 4 different shuttle
    types: Standard, Locking, Floating Horizontally & Floating Vertically .
    Could you tell us which ones you're using, and their lengthes?

    Thanks a lot and congratulations

    Nelson



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    Thanks for your comments Nelson. I'm far from a master machinest though. I've had a small CNC for two years, and still have quite a lot to learn. It hasn't been until recently that I've learnt enough to take on this project.

    I am using the Drylin T Series rails.

    X-Axis (long one)
    Drylin T Linear Guide, TS-01-15-600
    Drylin T Linear Carriage, TW-01-15

    Y-Axis
    Drylin T Linear Guide, TS-04-15-300
    Drylin T Linear Carriage, TW-04-15

    Z-Axis
    Drylin T Linear Guide, TS-04-12-300 (two lengths cut 68mm long)
    Drylin T Linear Carriage, TW-04-12

    All carriages are fixed bearing type, not floating.

    The big X-Axis carriage has adjustment control. The Y-Axis is a great fit. I am rather unimpressed with the small Z-Axis carriage though, an unacceptable sloppy fit. Only have one of those to start with. I've removed the bearing surfaces and plan to tap eight set screws in place to give the needed fine adjustment tuning.


    scsi... you've convinced me to change to the NEMA 23 for the X. It's big and insanely fast... gave it a test run on the bench with no load. If the belts could handle it, I could see it traversing the board from start to stop well within a fraction of a second

    Attached Thumbnails Attached Thumbnails Eclipze's SMD Pick'n'Place Build....-eclipze_pick_n_place_10-jpg  


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    This looks good...I am in to see how it goes

    Russell.



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    Hi,

    An interesting design, but I can't see how you won't get bouncing of the head at the unsupported end of the Y axis.

    The faster it moves the more momentum you have to deal with. When you stop the head, the energy needs to be dissipated some how.

    I guess time will tell.

    Cheers,

    Peter.

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    Nice work Eclipse! I think the design has many great ideas.

    However, I'm bit suspicious about accuracy of Drylin combined with stepper and belt drive. All of them are quite inaccurate devices in some circumstances. You may end up having only 0.5 mm accuracy. I woud use at least some preloaded ball rails and servos to get within 0.1mm. Also speed can be much higher with servo as you can push it to limits without worrying losing steps.

    I'm also starting to design a pick'n'place machine at my work. Instead of SMD it will be handing unmounted laser chips and doing automated testing on them. It has great accuracy requirements but speed is less critical. It will use machine vision to pick-up parts precisely.



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