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  1. #1
    Join Date
    Jul 2011
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    Open source P&P revolver head

    I like to share some insights on a multiple nozzle revolver head.
    This is just a drawing and I have no intention to build this. However, I will assist whoever wants to build one.

    Starting with a 5 mm thick plate, which is covered with another 1 mm plate I attached a disc stepper to it.
    At the front side I have a circular track with two openings. At the lower opening the head segment will exit here for Z-motion, to the right the head segment will engage with a stepper motor for nozzle rotation.

    The plate is milled out with two paths, one for vacuum (air/kiss) in the lower pick position, one larger one for the rest of the nozzles.
    I've designed an eight nozzle head, but any other number is feasible.

    The lower hole for vacuum has a 3 mm opening, all other 2mm.
    At the end of the path, I will attach vacuum generators. Likely one for pick and place and 3 for the other.

    The wheel hub is two parted. The longer one is attached to the motor shaft and the "star wheel", the shorter containing 8 3mm tubing will slightly press on the plate via spring tension.

    I've tapered all holes in the Nylon or Teflon wheel, in order to assure the vacuum will not drop, when the wheel turns.
    Attached Thumbnails Attached Thumbnails revolve1.jpg   revolve2.jpg   revolve3.jpg   revolve4.jpg  


  2. #2
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    Jul 2011
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    Front and rear of the revolver head.

    There are two discs spaced out by 20 mm. At the front side, I have the tubes coming out from the segments, which will be connected to the tubes from the wheel hub via silicone tubing.

    From the rear side we can see some pins sticking out with small bearings, which will engage with the circular track of the main plate.
    Motor driven levers will engage with these bearing at Z position and at the rotating station a segment will be pushed out by a few mm in order to rotate the disc with the nozzle plunger, by yet another stepper motor.

    I'll stop here for a few days, attending some other business. However, I'll be reading any feedback.
    Attached Thumbnails Attached Thumbnails revolve5.jpg   revolve6.jpg  

  3. #3
    Join Date
    Feb 2007
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    88
    Facinating.....I can see how the vaccum is acheived. But I am still confused about how the rotation of each nozzle is done.

    I guess from what you have written, it is locked into position by friction and a spring, and when it is pushed out by a few mm it is unlocked. I am also confused how the rotation station engages to perform the rotation.

  4. #4
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    Jul 2011
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    Yes, you are on the right track.
    In a hurry I couldn't find a longer spring, but I guess you get the idea.
    There are two bushings with a pretty tight fit, that we don't get much of an air leakage. The hollow shaft is forced against the lower bushing (with the right spring size).
    Upon nozzle rotation at the turning station a stepper motor shaft with a friction wheel (O-ring), which will be located perpendicular to the disc from the segment, will push back on the disc, than rotate the disc with nozzle and then the segment will be moved back to the track.
    I'm designing all this as I write. Please be patient.
    Attached Thumbnails Attached Thumbnails revolve7.jpg   revolve6.jpg   revolve8.jpg  

  5. #5
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    Jul 2011
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    In my ACAD design, I implemented the location of the stepper motor shaft for nozzle rotation. I'll likely select one NEMA 14 or even smaller.
    I also found that the track opening is in the wrong location. I'll change that as well.

    Than I'll add the Z-motor and the small motor, which pushes the segment out at the turn station. I guess a smaller 25 mm tin can stepper with gear head will do for both of these jobs.
    At the end of the gear shaft, I'll mount a lever, which will require only a few degrees of motion for Z and towards the theta motor shaft.

    Again, this drawing is evolving and it will change a few times. Particular the main plate will change with motors and component camera added.
    And, of course I also do mistakes here and there.

    Hope, my drawings explain better than I do.
    Attached Thumbnails Attached Thumbnails revolve9.jpg   revolve10.jpg  

  6. #6
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    Jul 2011
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    I placed 3 NEMA 11 motors in proximity in order to drive the Z axis, theta of the nozzle rotation and one driving the segment against the rotating station.
    Since I'm more inclined using servo motors, could you guys telling me what you think is a good speed I could be driving the steppers with?
    If I expect 5 rev per second, that makes it one in 200 ms, so if I rotate the nozzle by 180 degree, I could get this in ~ 120 ms (100 + ramp up and down).
    Most often the nozzle rotation does not impact the machine performance, if we rotate only by a few or 90 degree. For pushing the segment against the rotating station, I should expect 20-30 ms.

    Else, I designed for an 18 mm Z-stroke. In practice Z-travel should not require more than 12 mm. If I want to get 100 ms out of Z travel, I should rather count 40 ms up, 40 ms down and 20 ms for the air kiss.
    If you guys could confirm these numbers, than I can continue in my design.

    Also, I hope you are ready writing software code for this head. Keep in mind, while one nozzle picks a component, another component is likely in 12 o'clock position for camera inspection and yet another component at 3 o'clock for final rotation from the two previous camera inspections.
    Attached Thumbnails Attached Thumbnails revolve22.jpg  

  7. #7
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    Jul 2011
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    .. by the way. You can't pick all 8 components on the first path. You can pick only 7. Then the head has to travel with the PCB camera to the fiducials, calculate the theta offset of the component, which is currently in the rotating station, then rotate this component, advance the revolver by one step, rotate and inspect the next component. Upon the next cycle you have one component in placement position and now you do everything synchronous, placing, inspecting and rotating.
    It would be first hobby chip-shooter in the market. Good luck.

  8. #8
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    Jul 2011
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    While waiting on you guys to confirm stepper speed (and while my wife is writing school report cards) I made provisions for the Z-axis.

    Using a 3 mm shaft, I did cut some grooves and pockets into the main plate.
    At the lower end of the shaft I have a small plastic piece receiving the bearing of the segment at 6 o'clock and at the upper end I have a piece, which will receive the bearing of a cam, activated by the Z-stepper-motor.
    I also made two pocket for linear bushings or bearings.
    For betting viewing I removed the rear 1 mm cover plate.
    Attached Thumbnails Attached Thumbnails revolve33.jpg   revolve34.jpg  

  9. #9
    Join Date
    Feb 2007
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    88
    Let's see if I understand this correctly so far.

    In the last picture, I can see two slots in the circular ring where the bearings for each nozzle station ride. The one at 6 o'clock is to allow the nozzle to plunge downward. Then there is the one at 3 o'clock. It would seem the motor above the rotation motor must move the nozzle station outwards towards the rotational motor, rather than moving the rotational motor towards the nozzle. Correct?

    I am a little confused about the stepper motor that drives the z-axis. It is pictured at the top, but I do see any mechanism to push down on the nozzle. Is it hidden, or not yet drawn up? Edit: Ha ha. You posted while I was posting.

    >>>Since I'm more inclined using servo motors, could you guys telling me what you think is a good speed I could be driving the steppers with?

    It sometimes is a trial and error thing. By selecting a low inductance stepper and higher driving voltage, (say around 2-3 mH and 48V), you can get pretty good running torque at higher speeds. Off the cuff I'd say, (don't quote me on this): 20 rotations per second is about what you can safely expect, and still have about 35% of its rated standing torque. I would expect anyone that actually makes this head would either use servos, or wouldn't care if it doesn't operates super fast with steppers.

    Some other observations. Is it correct to say that revolver head chip shooters are mainly used for quickly placing bypass capacitors and resistors, and other non-fine pitch components. I ask this because I just don't see how this would be capable of placing a large BGA with just a friction based rotation station and non-closed loop vision inspection. It would seem that you'd want to vision check it again after the rotation. I've never been in the industry, so please forgive my ignorance.

  10. #10
    Join Date
    Feb 2005
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    122
    Quote Originally Posted by stewi View Post
    This is just a drawing and I have no intention to build this.
    What a pity that you don't intend to build it.
    I see that you're so opinionated about this.

    I would be interested to give it a try but I am pretty sure that it's not that can be done in a home workshop.

    Kind regards,
    DAniel

  11. #11
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    Jul 2011
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    Quote Originally Posted by Nails View Post
    Some other observations. Is it correct to say that revolver head chip shooters are mainly used for quickly placing bypass capacitors and resistors, and other non-fine pitch components. I ask this because I just don't see how this would be capable of placing a large BGA with just a friction based rotation station and non-closed loop vision inspection. It would seem that you'd want to vision check it again after the rotation. I've never been in the industry, so please forgive my ignorance.
    We (at Siemens) have never used closed loop vision system. Once the component was inspected, the head traveled full speed to the placement.
    I was targeting components up to 24 mm square.
    Yes, you can do fine pitch with the rotary head.

    The name "chip shooter" is likely reserved by turret head placement machines, which have a stationary rotary head and moving X and Y PCB to be populated. Fastest I've seen does one component every 0.09 second! However, these machines almost disappeared from the market. Nowadays, even Panasonic copied the Siplace head and this is mainly, what you see in China now.
    If you search u-tube you'll likely find a video from Siplace placing smaller components with a 12 nozzle head and larger with a 6 nozzle revolver head.

    In order to avoid confusion with the name chip shooter, I will from now on only use the name rotary head or revolver head machine.

    Thanks for the feedback on the steppers. I will count on 8 rev per second safe speed.

    Yes, we posted to the same time. Looks like, I got you hooked. Now, that you see the Z-axis, yes I will push the segment out to the turning station.

  12. #12
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    Jul 2011
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    Quote Originally Posted by dandumit View Post
    What a pity that you don't intend to build it.
    I will not totally erase that thought.
    If somebody pays me to build this head, I would do.

    Regards,
    Stefan

  13. #13
    Join Date
    Sep 2009
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    119
    Quote Originally Posted by stewi View Post
    ...The name "chip shooter" is likely reserved by turret head placement machines, which have a stationary rotary head and moving X and Y PCB to be populated....
    That's what I thought as well, but also heard many times a machine being called a chip shooter to designate a particular machine in an assembly line where there is also another machine(s) that is dedicated to place odd shape and high pitch components. In those cases the "chip shooter" was either an eight-head or a rotary head used to quickly place small passives.

  14. #14
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    Jul 2011
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    "chip shooter" is not in Wikipedia, so I take your word for it.

    By adding the turning station, motor mounts and cams, I wrap up this project and return to paid business.
    Whoever wants to build this, I will provide logistic support and step drawings.

    Multiple nozzle heads will also require:
    Fast automatic component feeders
    Feeder set up optimization software
    Tricky multitasking software
    Large air compressor for hungry venturi generators
    Hefty gantry and motors on a solid machine base.

    With multiple nozzle head, regardless if in-line or revolver, we get likely a gain in 50% machine performance, from single nozzle.
    Adding another gantry will add another 90%.

    For Nails and others, I would propose again a dual gantry and one nozzle each head.
    The design is fairly easy, even with nozzle changer.
    The gantries are light weight and can likely be designed as a table top machine.
    The feeders are not demanding high speed.

    However, it was a fun project for me and I love to be involved in this technology.
    Attached Thumbnails Attached Thumbnails revolve40.jpg   revolve41.jpg   revolve42.jpg   revolve43.jpg  

    revolve44.jpg  

  15. #15
    Join Date
    Feb 2005
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    122
    Like you have presented it until now seems to be doable by a hobbyist ...
    I see it like a lasercut base board and few stepper on it. I suppose that troubles are coming on the moment when you start to build the nozzles mechanism.

  16. #16
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    Jul 2011
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    Getting started could be a big hurdle too.
    I am only proposing a design plan, which can be modified.

    Also, I am a great fan of this open source concept. We could discuss any obstacles in this project and help each other to resolve issues.
    I have quite some knowledge about failure analysis http://www.steering-inc.com/about.html but admit finding bottlenecks in my own design is most difficult.

    However, I don't mind critique if it is constructive.

    Here is another thought of building the "star wheel" with 4 mm linear shafts.
    Attached Thumbnails Attached Thumbnails revolve50.jpg  

  17. #17
    Join Date
    Feb 2007
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    88
    I don't know whether to thank you or curse you for this information. I've been going round and round with ideas about how to make things a little better and easier for building. But I keep coming back to the conclusion that many elements of this design do indeed work out the best.

    Things I have changed are using 7mm wide linear rails/blocks to guide the nozzles, air cylinders for the up/down motion and rotational station engagement (with linear rails), timing pulleys and belt for the rotational motion, and an encoder on the shaft so I can use the index pulse to know the orientation at start-up. I still have details to work out, so I can't post a picture.

    I have a few questions.

    How small were you able to get the revolving wheel? I've gotten it down to 4 inches. With my lightning nozzle holders and nozzles hanging off of it, it ends up being just shy of 6 inches from tip to opposing tip on the other side. I can't see it getting any smaller.

    About fine pitch components; I found some Siemens literature that says the rotational accuracy for the 12 station head is +/- 0.7 degrees, and the 6 station head is +/- 0.3 degrees. It appears the rotational accuracy of the rotary head design is a function of the disk diameter located on the nozzle.

    http://www.automation.siemens.co.uk/...0606_final.pdf

    So there is some limitations for very fine pitch, large BGA's such as FPGAs. Hence the option of the "TwinHead" mechanism for these parts, which has +/- 0.07 degrees accuracy.

    The spring on the nozzle...it doesn't make much sense to me for how it is drawn. Can you include a post showing a transparent body housing with the bearings and spring?

    About only picking up 7 components on the first round. You could check the fudicials first and then load the parts to avoid this. But I suppose this is just an optimization so you can already pick up parts while the next board is loading, right?

  18. #18
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    Jul 2011
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    Looking at the wire frame ACAD drawing, I get a 142 mm diameter. 4" is very nice.
    I anticipated a spring which forces the pins in the hollow shaft against the lower bushing. Upon placement, pick up and rotation pin and shaft will deflect the spring.

    Wish you'll a happy and successful new year!!
    Attached Thumbnails Attached Thumbnails revolve20.jpg   revolve21.jpg  

  19. #19
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    Jul 2011
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    Adding one more thought to your discomfort.
    Although I like the idea with linear tracks and re-circulating ball carriers, it makes the head quite expensive and heavy. I would rather consider less expensive slides and easy head exchange feature. Ideally you plug the entire head into a single connector, using alignment pins and a single latch holding the head in place.
    Into the same place you can plug in another spare head within seconds or even a single nozzle head, while maintaining the other head.
    If your placement head becomes too expensive, you'll likely not effort an extra head.

  20. #20
    Join Date
    Feb 2007
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    88
    Yeah, linear tracks add about $450, but the added precision and virtually frictionless travel are appealing to me. I was afraid there might be a chance for binding without it, as the extending air cylinder (in my modified design) needs to be offset from center and spring loaded.

    >>Ideally you plug the entire head into a single connector, using alignment pins and a single latch holding the head in place.

    Definately one more thought for my discomfort.....I'm not sure I want to tackle that.

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