Avoiding jams in telescopic tracks

This topic has 19 replies, 9 voices, and was last updated 14 February 2016 at 12:39 by John McNamara.

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10 February 2016 at 19:10 #224786
John Munroe
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@johnmunroe13164
Hello

I'm trying to design a small metal telescopic track (6cm x 2cm when extended) where small objects may be arbitrarily positioned inside. Here's an example:

In the above example, the green block jams the tracks as the bottom cannot move upward. Does anyone know of a better design such that the tracks won't be jammed? I've thought about putting a sleeve on the inside, but if it was 6cm long and covers the entire extended length, it'd overhang when retracted.

Any help will be appreciated.

Thanks
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10 February 2016 at 19:10 #7999
John Munroe
Participant
@johnmunroe13164
10 February 2016 at 19:25 #224789
pgk pgk
Participant
@pgkpgk17461
can you simply reverse the system and have the wide end as the discharge end..any 'jams' hopefuly being discharged on withdrawal.

Or if you don't need access to the top of the shute then a sprial with a flexible inner sheath?

Or is it acceptable to have an upward or downward folding hinge midway?
10 February 2016 at 19:48 #224798
John Munroe
Participant
@johnmunroe13164
Posted by pgk pgk on 10/02/2016 19:25:52:

can you simply reverse the system and have the wide end as the discharge end..any 'jams' hopefuly being discharged on withdrawal.

Or if you don't need access to the top of the shute then a sprial with a flexible inner sheath?

Or is it acceptable to have an upward or downward folding hinge midway?

Unfortunately both ends are supposed to be used for discharged.

The setup is rather small, so I think hinges will fit in there.

I'm not sure if I completely understand, but how does a spiral work here?

Thanks
10 February 2016 at 20:03 #224802
pgk pgk
Participant
@pgkpgk17461
I had something like a spring type spiral supporting an inner flexible liner (so it's a tube when extended) then control it in various ways..perhaps as simple as a thread and rotating nut under the permanent section so it concertinas when closed.
10 February 2016 at 20:08 #224803
Danny M2Z
Participant
@dannym2z
Hi John.

Would a bevel on the inside edges of the smaller channel section be of any use?

* Danny M *
11 February 2016 at 07:29 #224848
John McNamara
Participant
@johnmcnamara74883
Hi John

The green part is behaving in a similar way to the wedging cams in a Sprag clutch. A little friction and the very powerful wedging action takes over.

**LINK**

I can see this problem happening not only with one part but 1.5 parts or more as well. They can press against each other and you have a jam.

Have you considered a spring loaded roller blind type base for your conveyor with guides each side to stop the parts falling off? Ideally the guides should taper wider in the direction of travel to inhibit any wedging action.

It would help if you defined the problem in a little more detail.

Regards
John

Edited By John McNamara on 11/02/2016 07:30:30
11 February 2016 at 13:48 #224889
John Munroe
Participant
@johnmunroe13164
Hi John,

I've thought about a blind type base, but I worry about wear and tear as the base would need to be rather thin to keep the small package.

These are actually parts of two parts that are separated by a spring. The spring is compressed when the two parts are pressed together. Inside the chutes, there can be arbitrarily positioned blocks. I wonder if the jamming issue could be resolved by giving the chutes a better finish, e.g., 1.6Ra? Perhaps, the gaps between the two could be reduced? Would it be reasonable to make the gaps 0.05MM on each side (so that lubricant won't get squeezed out)?

Thanks

John
11 February 2016 at 14:50 #224908
John McNamara
Participant
@johnmcnamara74883
Hi John

I doubt if polishing will be the answer as the action of the parts sliding will scratch the surface.

Trying to think outside the square??

You mention a spring is it steel? can it be attracted to an electromagnet attached to an air cylinder powered arm that could be programmed to pick the part and then drop it across the gap?

Assuming the pressed together parts are locked together and do not easily come apart could a vacuum system be used to simply suck them up?

Could the part be blown across the gap with compressed air into a wide funnel ?

Regards
John
11 February 2016 at 15:30 #224920
Neil Wyatt
Moderator
@neilwyatt
Pez dispenser?

Neil
11 February 2016 at 17:17 #224937
mark costello 1
Participant
@markcostello1
Could You put a double thickness of material 0n the sides of the small slide and mount it underneath?
11 February 2016 at 20:13 #224965
frank brown
Participant
@frankbrown22225
use two square sections each with both ends cut into fingers, so the fingers 100% interlock when closed up and you get gaps at the ends of the fingers when the gizmo is extended.

Frank
11 February 2016 at 20:34 #224975
frank brown
Participant
@frankbrown22225
Suggestion #2

If you need to keep the general shape i.e. a small one inside a big one. Then fix a couple of wires to the end of the small section on each end face and mill a couple of slots per side and bottom of the large one. Use a slitting saw so the hole is smaller on the inside. So now with the hopper in either of its position, at the transition the cargo will ride along the two bits of wire under it and guided by the bits of wire on the side, but as these have no sharp transitions, the cargo will travel smoothly along.

Frank
12 February 2016 at 17:53 #225081
John P
Participant
@johnp77052
Hi John

If you can re-work the track so that it is inclined by 45 deg
as in sketch in album (track) any parts will fall and be guided
by the vee ,by having the angle less than 90 deg will keep square
parts from settling in the vee ,providing that the track is folded from
thin sheet metal a longitudinal scarf will deflect parts over the step.
See sketch in album (track) .

John
13 February 2016 at 10:04 #225144
John P
Participant
@johnp77052
Hi John

From my previous post i realised that i had made
an error as having the track cut as a scarf joint one
edge would be facing down and could trap an object
between the joint and bottom of track.The drawing is
amended ,the top track is cut to a point at the lower
edge the angles should be staggered or different angles
so the object would only contact one at a time.

In any event with all the suggestions presented in this thread
some experimentation will be needed to get to successful
outcome.

John
14 February 2016 at 07:15 #225270
John Munroe
Participant
@johnmunroe13164
Hi John,

Thanks a lot for the drawing. Is the view on the left meant to be a cross-section of the track? If so, is it meant to be of a trapezoidal shape? That is, a wide bottom and a narrow top. Could square objects end up being wedged though, given that the edges exert higher pressures than faces do?

Thanks

John
14 February 2016 at 09:31 #225277
Neil Wyatt
Moderator
@neilwyatt
Much depends on the shape of the parts and how they can interact with the tubes. Would round tubes be less liable to jam?

Neil
14 February 2016 at 10:12 #225288
John P
Participant
@johnp77052
Hi John

The view on the left is the end view of the channel.
I would think the best way to make these would be to use
some thin sheet metal.
Yes the angle at the bottom is intentionally less than 90 deg,
square shapes will not sit then down in the bottom.

To some extent you would have to make some test pieces to
try out how effective something like this would be.
As there is no indication as to how the items in the channel are
moved along in either direction it would be difficult to know
how much force is available to overcome the junction.
Obviously the more shallow the front angle on the top part of the
channel the less the force would be needed to pass over it.

As you first indicated the extended length is 60 mm which
would imply the the closed length could not be less than
about 35 to 40 mm with some overlap of the two halves when at full
extension and at 20 mm wide whatever is in the channel is not
going to be that heavy.

Hope this helps.

John
14 February 2016 at 11:33 #225303
Clive Hartland
Participant
@clivehartland94829
Everything I have seen has a vibrating effect to stop or dislodge jams. Surely there is some way of oscillating the set up for that purpose?

Clive
14 February 2016 at 12:39 #225322
John McNamara
Participant
@johnmcnamara74883
Hi John

I actually have a couple of vibrating feed units, they came from a company that made telephones. There were robotic workstations with pick and place units. The parts were fed from a sorter onto long open tracks that presented them the right way up to the pick and place unit.

Each track had a vibrating unit underneath it, The units are quite simple although fairly heavy
Basically just a solenoid made from "E" lamination's and a straight bar of "I" lamination's spaced a few mm away
The Base has the E side of the circuit attached and the vibrating member the I They are joined by flat spring steel flexures. in a parallel motion There is also a simple controller to control the amplitude of the stroke.

The motion imparted to the parts was quite strong. Imagine a Z linkage and imagine the the solenoid applied a force in line with the upper horizontal line while the lower line was fixed to the base The height of the z would change and the line would move slightly forward causing an object on top of it to lift and due to friction between it and the line to move forward. repeated many times a second the parts move quite well. there being little friction in the opposite stroke direction as the line travels down and away from the part (which also has some remaining inertia) there is less force on it.

I guess you would not make one yourself anyway there are many suppliers.

The Pair i Have are destined for a shaker table to cast epoxy composite parts on. They are quite massive and must have been made for large objects.

**LINK**

Regards
John
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