Ratcheting parts feeder

[Anthony Webb]

I spent some time playing around with various feeder designs and came to the conclusion that I needed a little more from my feeder.  The feeder Alex posted was probably the best one I tried, and, although it fed parts fine, it was one viable for paper tape stuff, which is only a portion of the parts we use.  An additional dealbreaker was that the mechanics of that feeder sit above the table high enough that the heads of the machine could interfere, or, the push rod needed would have to be overly long to accomodate.

So I went back to the drawing board, I knew I wanted something with the mechanics below the parts as not to interfere.  I also wanted a design that would engage the holes on the tape and keep them engaged.  A ratcheting mechanism seemed like the best way to make this happen.  I'm going printing some parts tonight to see how durable and what kind of fit is there.  For tape peeling I am going to do the finger that lifts half of the tape and folds it over, revealing the part.  That still needs to be designed, and my 3D skills are so sub par this is taking forever, but I am getting there.  Here are some shots:

[Anthony Webb]

Meant to explain a few things.  The large holes you see are there for small RC bearings, there are 3 of them, one on the main large gear assembly.  One in the center of the arm, and one out on the end for the ratchet.  I want to be able to tighten everything down good with M5 hardware, and have it rotate freely too.  RC bearings are not too expensive.  The back will be open so you can slide you finger in and detach the ratchet and pull parts out and feed new tape in.  Most of the stuff we do is not on full reels, just really long cut tapes.  I noticed in the side view image I posted the arm was in the path, that has been fixed.

[Michael Anton]

According to the other thread that discussed that tape peeling method, it would appear that that method is patented.  You may want to be careful using that.  Perhaps examining the patents would yield a solution that does not infringe, or at least confirm if it does.

Mike

On Friday, October 14, 2016 at 10:03:16 PM UTC-6, Anthony Webb wrote:

[Jon Raymond]

Patents are only an issue if you are trying to commercialize the feeder.

[Anthony Webb]

Printed gear appears to be a winner. That was really the only concern. I think the rest of the design should work well. I have not looked into the patent too much I'm mostly interested in solving this for myself but if anyone has ideas they'd like to see me try for peeling let me know. 

Sent from my iPhone

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[Gregory Davill]

Nice work! That gear looks like it's turned out perfectly.

I'm curious about the ratcheting mechanism, does it have the same number of teeth as the outer sprocket?

[Anthony Webb]

Thanks Greg.  It does have the same number of teeth, 55 to be precise :)

I have the model a lot further along now.  I am shooting for 13mm wide for the final assembled 8mm tape feeder, which is about as narrow as I think I can hope for.  You can now see in the model how I intend on attaching the spring.  The 3 bearings will be press fit so no fasteners will be needed.  Bearings wont be here until next week unless I can find some at a local hobby shop tomorrow.  I am going to print some more of the parts.

[Michael Anton]

The general consensus in other threads that have discussed this type of situation would beg to differ.  Most patent law prohibits making or using patented technology, even if not for commercial gain.  Wikipedia describes this pretty well: https://en.wikipedia.org/wiki/Patent.  IANAL, but this is what I've read, and it surprised me as well.

Mike

[Cri S]

Check 3d printed Feeder Response.

[Malte R.]

Hey Anthony,

looks great so far and congrats on the nice 3D printed parts :-)

How do you intend to make sure that the tape is always advanced by the same distance? Just by controlling the head movement?

On Alex's feeder, there is a mechanical endstop for the pin, so end position will always be identical.

Karl, who also uses a ratcheting mechanism, has a blocking mechanism which inserts a pin into the sprocket hole at a deterministic locatrion:
http://www.knasmusic.com/diyeverything/pickandplace/tapefeeders.php

I'm also curious how you'll solve the cover tape peeling; will wait for the next pictures ;-)

Cheers
Malte

[Anthony Webb]

Hi Malte,

The arm bottoms out, and is pulled against the front holder with a spring.  This will keep the parts advancing to the same place again and again.  Also, the ratchet gears are in lock step with the 4mm pins on the end.  The only way things move forward is while the ratchet is engaged, and since the tape is always engaged by multiple teeth everything *should* come back to the same place again and again.

I will say that I have no idea if this all will even work.  It makes sense in my head, but in practice everything may all fall apart ! :)  It's been good 3D modeling practice anyway.

Here is some more photos from around the thing in various stages of undress:

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[Anthony Webb]

Malte,  I have seen that feeder before, a couple things I was hoping to improve.  First, I'd prefer to use my X/Y motion to bump as opposed to my Z.  Second was that in his design if the parts are farther apart you have to hit the advancement multiple times (if I understand the motion correctly?)  In my ratchet system you can advance MULTIPLES of exactly 4mm by bumping farther.  This means that if parts are 4mm apart, or if they are 12mm or even 16mm apart a single bump will move you.  But alas, his feeder actually works and I am still waiting on bearings so we'll not count our chickens before they hatch. 

[Anthony Webb]

A couple more parts hot off the press. Everything I have been printing (main gear included) at .2mm layer height and 20% infill. The printer prints great to .5mm layer height but for quick iterations .2 seems to be more than sufficient. 

Printing these tape hold down tabs and peeler into the end cap is probably not a good move as it doesn't adjust well. I am thinking of doing loading those for a snug fit no matter what tape thickness (paper/plastic) that you feed. 

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[Malte R.]

I think I understand your design better now.

Basically, the end position of the lever is also fix - and depending on how far you push the lever, the ratchet will lock into one or multiple teeth further from the start position; and when returning advance the tape by increments of 4mm - correct?

You are also spot on about Karl's feeder. It will only forward by one sprocket hole / 4mm and will need multiple pushes to further advance the tape.

XY vs. Z movement has pros and cons; probably depends on the machine a lot. On small machines, Z might have advantages; on others XY is fine.

An interesting idea for XY might be adding another linear rail with an actuator to one side of the machine; so the feeders could be advanced independently from the head.

But first things first. Besides the cover peeling an interesting details to think about will be supporting tapes with different thickness. Paper tape will be significantly thicker than embossed plastic tape.

I think to support both, you will either need some sort of spring to hold the tape down or design some mechanism to push the tape up; which would be my preferred approach.

Regards
Malte

[Anthony Webb]

You are understanding the design well malte.  I am scheming a better way to hold down the tape. Holding it up from the bottom is hard because some parts are in deep pockets, so I think I will first try either a springy top cover or if I could find a foam wheel I think that would work nicely too. Most of tinge tape I have measured is under 1mm so foam would soak that up nicely. 

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[Michael Anton]

Plastic tape can be quite thick, if you include the pocket depth.

On the design I'm working on, I have a U shaped channel that the tape rides on, that provides clearance for the pockets.  It is spring loaded from the top so that it accommodates various tape thicknesses.  You will want to have this too, as it keeps the tape steady during advance, and picking, so that there is less likelihood of the parts jumping out of the tape.  Plastic tape seems to be the worst for this.

I think your little ratchet pawl is going to need a spring on it to press it against the sprocket.  At least that is how I've always seen it done.

Mike

[Anthony Webb]

I have the same U shaped pocket for the parts, so I will likely be looking at options to keep the ape down from the top.  I had hoped that if I had a nice bearing that gravity would cause that ratchet to fall down.  Now that I have printed that part and played with it I think you are most likely right, gravity more than likely isnt going to be enough force, even with a nice bearing, that little ratchet is just not heavy enough.  Should be a pretty easy fix though.

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[Malte R.]

What if you modelled the U-shaped guides as a separate part that could slide up and down?

Then you could use a compression spring to push it (and the tape) upwards against the plate which covers the part pockets after the cover tape has been peeled off.

The pins on your sprocket wheel should be long enough to still advance both thin plastic and thicker paper tapes.

One more concern: You don't want the tape to move vertically when the nozzle picks up a part, otherwise other parts may jump out of their pockets.

This might work witht the spring-loaded guides mentioned above or may require a different solution for the pickup location. Maybe an exchangable guide (different plugins for thick and thin, flat and embossed tapes) is the easiest approach.

By the way: Are you willing to share and collaborate your design in Fusion 360 cloud? That way we could branch off your parts and directly model ideas like this one...

[Malte R.]

Oh, and for the ratchet you may want to look into using a tiny torsion spring to push the ratchet agains the wheel.

Something like this:
https://us.misumi-ec.com/vona2/detail/110302306960/

[Anthony Webb]

For the ratchet I am going to try a simple chunk of latex tube resting against the ratchet, should be plenty of force to kick it over.

I will definitely be sharing this in the fusion cloud.  My 3D modeling skills are so raw, and terrible, not sure how beneficial to people these butchered models will be.  I'm more of a brute force kind of guy, I envy some of you guys who can whip this stuff out so fast and elegant.

I may try to use spring steel like Alex did for holding down his tape on the in-feed side, still need to brainstorm some on the tape lifter and folder.

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[mojalovaa1]

Can you please give  me that model on IGS files or STL , only for see something , I think that  you have  so big space  on top side on the feeder , you will have big problems with component  jump  , if you are look  some  video  for feeder you can see that on rack side have  some pcs metal or plastic for cover it ?

Please look on this video : http://www.digitaltrends.com/cool-tech/chipsetter-one-kickstarter/

[mojalovaa1]

On 2.02 min

[Anthony Webb]

Hi Moja,

I will be releasing the model soon after I do some cleanup.  The free span distance you are referring to is ~20mm, the gear teeth will be supporting the tape somewhat.  I am not yet sure where I will be peeling the tape though, it may very well be after that span anyway.  Thanks for the heads up, I will keep a close eye and consider your feedback.

Regards,

Anthony

On Sun, Oct 16, 2016 at 3:13 AM, mojalovaa1 <moja...@gmail.com> wrote:

Can you please give  me that model on IGS files or STL , only for see something , I think that  you have  so big space  on top side on the feeder , you will have big problems with component  jump  , if you are look  some  video  for feeder you can see that on rack side have  some pcs metal or plastic for cover it ?

Please look on this video : http://www.digitaltrends.com/cool-tech/chipsetter-one-kickstarter/

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[alex]

Anthony, this feeder design idea is awesome! Can't wait to see it up and running!

[Malte R.]

Anthony, I would probably peel the cover at some point behind the sprocket wheel. I assume the wheel and free span will cause to much movement to keep the parts in place.

In some of your pictures it already looks like you have placed the "peeler" there. If you move that a bit further, you could also include some guides for the cover tape.

Then again, I'd apply pressure from the bottom with the U-shaped guide, so the pockets are fully covered once the tape is removed.

You could move the pickup location a bit outside the current dimensions. At the pickup location you need to support the tape so the nozzle does not bend it, push it down or cause too much vertical movement. Interchangable plugins might be a way to go - thinking of U-shaped guides of different height for plastic and a solid block for paper tapes.

These could probably just drop into a mating slot.

Cheers
Malte

[Anthony Webb]

The bearings came in and I spent a lot of time printing and reprinting small shafts and holes looking for the exact right press fit that was tight enough on the bearing to have no slop and not so tight that you had to destroy things to get stuff apart.  I'm really fond of holing parts together with press fit bearings.  Once they are honed in they offer a very tight, accurate, and smooth motion.  I am waiting on a chunk of latex tube to use to keep pressure on the ratchet, but for now the motion and assembly checks out with flying colors.  Will be moving on to how to hold down and peel the tape.  Found the perfect spring as well.  Here are a bunch of images:

[Danh Trinh]

Nice looking parts. Is this printed on a professional grade 3D printer? PLA or ABS? Did sprocket teeth need support material?

[Anthony Webb]

These parts are from a prusa i3 mk2 kit I built a couple weeks back. This is my 5th printer and I have always had a love/hate relationships with my printers (mostly hate!) I have never been very happy with print quality and certainly never been able to fire and forget prints. Well, with this mk2 I can say that my perspective has been totally changed. The prints are amazing, every single time. I can start a print and walk away and come back to a perfect part sitting on the bed. Not bad for a $699 kit!! No supports were needed for any of these parts, the were all printed in PLA at .2 mm per layer (this machine prints amazing down to .05mm!) 

Sent from my iPhone

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[Danh Trinh]

Good to know. I think I'll buy that printer now. Youtube reviews look good. Too bad there's a 3 week lead time.

[Daniel Dumitru]

I am looking for some time to this thread.

I think that some parts are better to be lasercutted - I am referring to sprocket.others may remain 3 printed.

Could you please send me 2 dxf's one with sprocket another one with "bits" ? I will try to cut it from plexiglass .

BR

DAniel

On Fri, Oct 21, 2016 at 11:48 AM, Anthony Webb <anthon...@gmail.com> wrote:

The bearings came in and I spent a lot of time printing and reprinting small shafts and holes looking for the exact right press fit that was tight enough on the bearing to have no slop and not so tight that you had to destroy things to get stuff apart.  I'm really fond of holing parts together with press fit bearings.  Once they are honed in they offer a very tight, accurate, and smooth motion.  I am waiting on a chunk of latex tube to use to keep pressure on the ratchet, but for now the motion and assembly checks out with flying colors.  Will be moving on to how to hold down and peel the tape.  Found the perfect spring as well.  Here are a bunch of images:

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[Anthony Webb]

Hi Daniel,

Model is coming, I need to prove a couple things and clean up all my dirty work a bit first.  But I will be publishing all my work.

For those of you interested in how I want to try and hold down and peel the tape, here is some screen shots of that.  Basically I am thinking a floating bar riding between endstops that is held in place by surgical tubing on either end (dont have that drawn yet)  Anyway, just an idea, throwing it out there without shame when it fails.  Its the simplest way I could think of.  I'm gonna print one and try it.

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[Anthony Webb]

Here is what the loops for the surgical tube will look like, one on each side.

[Gregory Davill]

I've also been watching your design unfold. I'm interested in making lasercut feeders, I made a proof of concept laser cut sprocket.

1mm Delrin/Acetal. Looks like it will work well. I've ordered spring pins, so I can mesh the ratchet to the sprocket.

Unfortunately the heat from the laser is warping the 1mm thick sheet, this pushes it out of focus. I'm adding air-assist to my laser cutter, which should help.

[Anthony Webb]

This is really cool Greg!  Hopefully much of what I am cooking up here will translate well for you, and I am hoping that it works well enough that people will want to rally around and iterate to come up with something very reliable and affordable  that we all can benefit from.  I'll try and get the designs posted very soon.

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[DAniel Dumitru]

VEry interesting Gregory !
Could you please tell me how did you have generated that ?
I would like to try to cut it as well .

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[Anthony Webb]

This is the full concept.  Will try it out tomorrow, getting late in Idaho :)

[Gregory Davill]

I just modeled it directly in Rhino 5 (My goto CAD tool for lasercut stuff)

I'm pretty sure you could do it parametrically in F360.

For reference I've attached the one I cut.

[Gregory Davill]

Drafted up a parametric model of just the gear in F360. Go into the parameters window and you can adjust everything. (teethCount, pitch, toothWidth)

The tooth profile is just a rounded rectangle, good fro driving tape (not good for meshing with another gear.)

http://a360.co/2esQqos

Daniel, you should be able to export a DXF from the face of the gear for laser cutting. (I haven't tried cutting this out yet, but it looks about right)

Thanks,
Greg

[Anthony Webb]

Hi Greg,  Thanks for sharing this, I built mine the hard way, wish I had your 3D modeling skills!

I'd like to share with the group my design so those of you who would like to play with it can do that.  I made one pretty significant tweak where I joined the front and rear clamps into a single unit.  This means that the arm can be captured in a slot so it cant wobble at all.  We give up 1mm in width to do this but I think the end result is worth it.  Here is the link to the current state of the feeder: http://a360.co/2dKThrX

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[Malte R.]

Hey Anthony,

thanks for the updates and sharing the model.

I might be missing something, but I still don't see any mechanism to support the tape in the pickup location.

I am afraid the nozzle will bend it down and send all the parts uncovered jumping across the feeder?!

Also, I am unsure if the tape peel mechanism will work in the way it is designed. Have you had a chance to try it yet?

Cheers
Malte

[Anthony Webb]

HI Malte, 

Because the parts can vary pretty dramatically it would be difficult to support the bottom of the part pocket, so instead both edges of the tape are supported.  We have been doing this on our strip tape holders too without any issues, our strip tape holders also have the cover peeled back on the whole strip so if we were going to see problem with parts jumping out I assume we would have seen it there already.  But the supported edge approach is pretty proven at this point so I am not too worried about problems there.

The tape peeler is not proven at all.  It may not work.  Its just a first crack at something that aims to lift one side of the tape and pull it over to one side, exposing the part that needs to be picked.  I am in need of some rubber/latex tube to completely test the design.  I was not able to find any yesterday, but there is a medical supply and farm supply store that I think will have it, they will be open tomorrow.

Keep the ideas coming, as well as any questions or concerns, I'm hopeful we can make this design work but it make take several revisions.

Thanks,

Anthony

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[Malte R.]

Because the parts can vary pretty dramatically it would be difficult to support the bottom of the part pocket, so instead both edges of the tape are supported.  We have been doing this on our strip tape holders too without any issues, our strip tape holders also have the cover peeled back on the whole strip so if we were going to see problem with parts jumping out I assume we would have seen it there already.  But the supported edge approach is pretty proven at this point so I am not too worried about problems there.

I don't suggest supporting the middle of the tape. While this would work with paper tape, supporting the "bottom" of the pockets of embossed plastic tape in nonsense, as depending on the part these will have differing depths.

However, if you support the edges, you need some mechanism which either pushes the tape down or the guide up - so there is no vertical play.

In my strip feeders, this is done by the top guides and pressure is calibrated by screws holding it in place:



John took the opposite approach; in his strip feeder the guides push upwards aggainst a rail - but the principle remains the same:



If your design supports paper tape (which is significantly thicker than plastic tape), then the plastic tape will have vertical play between the upper and lower guides - that is the problem I wanted to point out.

 

The tape peeler is not proven at all.  It may not work.  Its just a first crack at something that aims to lift one side of the tape and pull it over to one side, exposing the part that needs to be picked.  I am in need of some rubber/latex tube to completely test the design.  I was not able to find any yesterday, but there is a medical supply and farm supply store that I think will have it, they will be open tomorrow.

I am keen to hear about your results. I assume that it is rather difficult to remove the tape that way. All the commercial feeder's I have seen pull the cover tape at an obtuse angle - and the (patented?) strip feeder add ons seem to have a very clever metal construction where a sharp- and durable edge peels the tape away.

Anyways, let's test and see.

BTW: There is a parallel discussion about strip feeders at LitePlacer forum. John and Juha are interested in making a "commercial" version of those with injection moulded parts: http://liteplacer.com/phpBB/viewtopic.php?f=11&t=399

[Anthony Webb]

I see what you are saying Malte.  In this case the tape is being held down much like your strip feeders.  There is the bar (that is also removing the tape) which is pressing down on the paper tape and holding it down.  The "spring" which secures the flat plastic tape but also "adjusts" for thicker paper tape consists of the 2 chunks of surgical tube which lay across the peeler bar.  Does that make sense?  I posted pics of that peeler bar and the holes above it to hold the rubber/latex tube which holds it in place.

I may replace out the surgical tube that holds down the peeler bar for actual springs that I can fine adjust.  There is a bit of a balance between the various pieces at play here.  First, the tape has to be held down with enough force that when the arm is pushed back it doesnt just pull the tape back.  But that down force also has to be light enough to be overcome by the spring on the arm which pulls the tape forward.

At any rate, we're learning!

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[Anthony Webb]

Made some more progress.  I printed up a fresh copy of the latest files and assembled up a unit.  "Assembly" was pretty much a non event, a couple minutes of pressing together a few parts.  The mechanics and tolerances work beautifully.

As expected, I hit a few snags trying to peel the tape.  I'll line out the hurdles I've hit:

-- Loading tape.  Right now loading tape can be a little problematic because as the tape approaches the teeth there is no way to tell if the holes are matching the teeth or not.  You can see it from the bottom but if the feeder was attached to the extrusion that might not be very easy.  Might need some cutouts to see the teeth to aid in loading them.

-- Overcoming friction.  The surgical tubing does a great job of holding down the tape, perhaps even too good of a job!  On thicker paper tapes it is almost so much that I dont know that I could fit a spring strong enough to overcome the friction.  Peeling the tape off the top with the spring will only add to the friction.  I'm still unsure what size of spring would give enough force, but this might be a real problem with my design in general.  I am going to lift the hold down tubing just slightly and get a bigger spring, we'll see what happens.

[Jason Parmenter]

Looks great!  Can't wait to try these out on our machine. They do make some thinner walled rubber tubing that can be found at sportsman's ware house. They use it for fishing and archery.  The tubing you are using is fairly stout silicone tubing. Anyways perhaps a thinner walled tubing would do the trick. 

On Oct 30, 2016, at 8:04 PM, Anthony Webb <anthon...@gmail.com> wrote:

Made some more progress.  I printed up a fresh copy of the latest files and assembled up a unit.  "Assembly" was pretty much a non event, a couple minutes of pressing together a few parts.  The mechanics and tolerances work beautifully.

As expected, I hit a few snags trying to peel the tape.  I'll line out the hurdles I've hit:

-- Loading tape.  Right now loading tape can be a little problematic because as the tape approaches the teeth there is no way to tell if the holes are matching the teeth or not.  You can see it from the bottom but if the feeder was attached to the extrusion that might not be very easy.  Might need some cutouts to see the teeth to aid in loading them.

-- Overcoming friction.  The surgical tubing does a great job of holding down the tape, perhaps even too good of a job!  On thicker paper tapes it is almost so much that I dont know that I could fit a spring strong enough to overcome the friction.  Peeling the tape off the top with the spring will only add to the friction.  I'm still unsure what size of spring would give enough force, but this might be a real problem with my design in general.  I am going to lift the hold down tubing just slightly and get a bigger spring, we'll see what happens.

On Sun, Oct 23, 2016 at 11:32 AM, Anthony Webb <anthon...@gmail.com> wrote:

I see what you are saying Malte.  In this case the tape is being held down much like your strip feeders.  There is the bar (that is also removing the tape) which is pressing down on the paper tape and holding it down.  The "spring" which secures the flat plastic tape but also "adjusts" for thicker paper tape consists of the 2 chunks of surgical tube which lay across the peeler bar.  Does that make sense?  I posted pics of that peeler bar and the holes above it to hold the rubber/latex tube which holds it in place.

I may replace out the surgical tube that holds down the peeler bar for actual springs that I can fine adjust.  There is a bit of a balance between the various pieces at play here.  First, the tape has to be held down with enough force that when the arm is pushed back it doesnt just pull the tape back.  But that down force also has to be light enough to be overcome by the spring on the arm which pulls the tape forward.

At any rate, we're learning!

On Sun, Oct 23, 2016 at 10:55 AM, Malte R. <malte...@gmail.com> wrote:

Because the parts can vary pretty dramatically it would be difficult to support the bottom of the part pocket, so instead both edges of the tape are supported.  We have been doing this on our strip tape holders too without any issues, our strip tape holders also have the cover peeled back on the whole strip so if we were going to see problem with parts jumping out I assume we would have seen it there already.  But the supported edge approach is pretty proven at this point so I am not too worried about problems there.

I don't suggest supporting the middle of the tape. While this would work with paper tape, supporting the "bottom" of the pockets of embossed plastic tape in nonsense, as depending on the part these will have differing depths.

However, if you support the edges, you need some mechanism which either pushes the tape down or the guide up - so there is no vertical play.

In my strip feeders, this is done by the top guides and pressure is calibrated by screws holding it in place:

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John took the opposite approach; in his strip feeder the guides push upwards aggainst a rail - but the principle remains the same:

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If your design supports paper tape (which is significantly thicker than plastic tape), then the plastic tape will have vertical play between the upper and lower guides - that is the problem I wanted to point out.

 

The tape peeler is not proven at all.  It may not work.  Its just a first crack at something that aims to lift one side of the tape and pull it over to one side, exposing the part that needs to be picked.  I am in need of some rubber/latex tube to completely test the design.  I was not able to find any yesterday, but there is a medical supply and farm supply store that I think will have it, they will be open tomorrow.

I am keen to hear about your results. I assume that it is rather difficult to remove the tape that way. All the commercial feeder's I have seen pull the cover tape at an obtuse angle - and the (patented?) strip feeder add ons seem to have a very clever metal construction where a sharp- and durable edge peels the tape away.

Anyways, let's test and see.

BTW: There is a parallel discussion about strip feeders at LitePlacer forum. John and Juha are interested in making a "commercial" version of those with injection moulded parts: http://liteplacer.com/phpBB/viewtopic.php?f=11&t=399

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[Peter Betz]

Hi Anthony,

 As i suggested before, why don't you try some closed cell foam "backer rod". It's available at most hardware stores in various sizes and I think it might be a better solution for your feeder as designed. Found in the weatherstripping aisle or concrete aisle etc. It will be easier to apply a lighter yet consistent force and there wont be much for sliding friction.

Something like these:

https://www.homedepot.ca/en/home/p.backer-rod-foam-insulator.1000156193.html
http://www.homedepot.com/p/M-D-Building-Products-1-2-in-x-20-ft-Caulk-Backer-Rod-71480/202066515
http://www.homedepot.com/p/M-D-Building-Products-1-2-in-x-20-ft-Caulk-Backer-Rod-71480/202066515

Peter.

[mojalovaa1]

Anthony when we can expect some video on work with that feeder ?

[Anthony Webb]

I will see if I can find some, thats probably not a bad idea.

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[Gregory Davill]

I agree, the tubing might provide a nice spring force, but the rubber creates too much friction. A foam might be better, if you can find something suitable.

I bought an air-compressor and upgraded my lasercutter with air-assist. Delrin (Acetal) now cuts pretty well, so I've modeled up a ratcheting gear parametrically.
To test it I designed a simple ratchet mechanism. Seems to work well, The Delrin can be used to create "living hinges" or flexures. This could have the potential to remove springs/rubberbands.

Files:
Parametric Gear (http://a360.co/2eUhRrd)
Assembly (http://a360.co/2eUgVTJ)

[Anthony Webb]

There is a misconception that the tubing actually rubs against the tape. The tubing actually simply hold down a plastic bar which puts force against the tape but doesn't actually provide any friction against the tape. 

The peel bar that I made out of plastic doesn't seem to be able to have a strong enough leading-edge to peel the tape. I am working up a new peeler that incorporates peeling with a metal front edge. I'm really happy with the ratcheting mechanism and it's ability to advance the tape accurately. Once I've got a peeler that works well I think we will have a winner.

Sent from my iPhone

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[Anthony Webb]

So I've been fighting passive tape pulling and have come to the conclusion (as many suspected) that doing that with 3D printed bits wont happen.  The sharp/flat surface needed is just not able to be rigid enough to get the job done.

The good news is that the motion itself is 100% reliable and accurate, this means that feeding can happen consistently without expensive or complicated indexing, light gates, etc.  Even sloppy movement to load the spring, will still yield parts that feed to the same place every single time.  I am very excited about that!

I'm exploring alternatives on how to peel the tape and am even looking at using a motor to do it.  If I go that far, I could also add an optional solenoid or motor to load the spring.

Question I have for you guys out there, is there a way electronically to tell how much load is on a small motor, I was thinking I could monitor it to be able to tell the motor when to stop peeling.  So as the tape advances and peels the slack would mean less load on the motor at which point the motor would kick on and load itself up again.  Is that possible?  I've seen steppers that have torque hold, which is essentially what I think would work for a tape peeler, but it would need to be small/inexpensive.  Any of you gurus out there have some suggestions?

[Graeme Bridge]

Anthony I would think you could use something like this

The AllegroTM ACS712 provides economical and precise solutionsforACorDCcurrentsensinginindustrial, commercial, and communications systems. The device package allows for easy implementation by the customer. Typical applications include motor control, load detection and management, switch- mode power supplies, and overcurrent fault protection. The device is not intended for automotive applications.

The device consists of a precise, low-offset, linear Hall circuit with a copper conduction path located near the surface of the die. Applied current flowing through this copper conduction path generates a magnetic field which the Hall IC converts into a proportional voltage. Device accuracy is optimized through the close proximity of the magnetic signal to the Hall transducer. A precise, proportional voltage is provided by the low-offset, chopper-stabilized BiCMOS Hall IC, which is programmed for accuracy after packaging. 

[Anthony Webb]

Thanks for the suggestion.  Thinking about this, perhaps all I need to do is just limit the current to the servo (maybe a POT to dial it in?) such that the servo only has enough torque to pull slack, and not enough to tear itself apart?

-Anthony

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[Oz-Ron]

To keep it simple & cheap perhaps a 555 timer could be employed to drive it by PWM?

Pretty sure the 555 output would be sufficient to drive a small motor directly.  Just use a pot to adjust the duty cycle and therefore the constant torque level. Plenty of proven 555 circuits to select from.

 

Ron

[Anthony Webb]

I started modifying the model such that the bar which holds down the tape no longer acts as a peeler, and instead I am peeling tape out the back.  Printing this revision now so we can validate that peeling out the back works with the design.  Hoping I can get a motor/spool on the rear to take up the tape eventually.

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