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  1. #1
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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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    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
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    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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    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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    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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    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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    .. 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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    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
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    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
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    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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    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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    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

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