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Old February 12th, 2009, 02:43 AM   #1
harrysts
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need Help, sensor for coconut

i want to make automate counter for coconuts fruit that using sensor to detect, ofcourse i use PLC.

the problem is i do not know what sensor i must use to detect this coconuts fruit. The photoelectric not work since coconuts not clean (still have the hair inside the outer shell), any suggestion from u guys ?
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Old February 12th, 2009, 03:52 AM   #2
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you have to explain in detail how the arrangement is? & how u going detect? etc..
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Old February 13th, 2009, 10:45 AM   #3
harrysts
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the conveyor runs by a motor that always on, and its conveying coconuts pass the sensor. I included a picture here.

ftol.JPG

in the left picture i'm using E3F4 omron photoelectric sensor, but each time a coconut detected - the result is not one (i mean more than one - i think this sensor read the hair of coconut).

in the right picture, is it possible to detect coconuts ? how ? and what sensor i must used?

this is the coconut picture :
scontoh2.JPG

i'm sorry if the picture is bad.
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File Type: jpg ftol.JPG (13.0 KB, 97 views)
File Type: jpg scontoh2.JPG (3.6 KB, 80 views)
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Old February 13th, 2009, 11:02 AM   #4
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If your process is like the second picture where all the coconuts are bunched up together then I think this will be very difficult to count. Can you get them to be transported down the conveyor in an orderly single file? Then the counting process will become much more simple. What type of PLC are you thinking of using? With some PLC types, it is possible to increment a value at the very edge of voltage detection, so when the coconut passes the sensor the system only see's one, when the sensor is clear the process is ready to be repeated, i.e. ready for another coconut to be processed. I would simply increment a word value(or double word value depending on how many coconuts there are!) at the edge detection (transition from zero 0v to positive +v input) from the sensor from a single file of coconuts.
one more thing, you need a gap between coconuts otherwise, the PLC will think its one big coconut, could be done by programming, but easier with gaps
hope this helps,

Regards,
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Old February 13th, 2009, 11:07 AM   #5
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The biggest consideration, by far, is whether or not there is only one coconut in front of the sensor at all times.

This is best solved by mechanical means and it sounds like you may already have that solved by looking at the left side of your first picture.

My first inclination would be to use a through beam photoelectric with a high excess gain to "see" through the hairs. For instance, if the conveyor is 18" across, use a through beam pair that has a range of 10 ft. (for example).

Then you should have some sort of time delay on the incoming signal before actually counting the coconut. If the sensor does pick up hairs, the signal is likely going on and off rapidly but when the hard part of the coconut is moving by the sensor it should be blocked for a solid amount of time. This time will depend on the size of the coconut and speed of the conveyor but, hopefully, you can find a time that senses the smallest coconuts at the fastest conveyor speed without triggering on the hair.

If you can guarantee some separation of the coconuts, you could put in a scale section and determine if a coconut is there by weight.

Ultrasonics might be able to see the nut without the hair but some testing would be in order before you would know if it will work. Usually a distributor or manufacturer will sample a sensor to you for a test.

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Old February 13th, 2009, 12:06 PM   #6
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Can you use a conveyor with dividers on the belt that are high enough and spaced so that only one coconut can be between two dividers? Then use two offset sensors. One sensor is triggered by a belt divider, the other by the coconut that would be between the dividers. Basically it divides the conveyor into coconut sized "boxes" and only when the "box" is centered on the PE do you check to see if the "box" has a coconut or if its empty.
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Old February 13th, 2009, 12:36 PM   #7
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How about an old fashioned limit switch with an arm that gets pushed by the coconut?
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Old February 13th, 2009, 01:06 PM   #8
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Hire an unregistered immigrant for 35 cents an hour to manually count the cocnuts.

There is probably some expensive machine vision sytem that might be able to handle this problem, but I think that mechanically seperating them is the best solution.

It seems like using an old fashioned mechanical limit switch would be just asking for trouble. No doubt it would get clogged with coconut hair.

A time delay off "filter" would probably solve a lot of problems with the cocunut hairs giving you jittery signals.

If you know the conveyor speed and the minimum and maximum coconut sizes, you can probably logically deduce if you got multiple coconuts being counted as one coconut.
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Old February 13th, 2009, 02:03 PM   #9
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make it single file and use reflective sensor (i prefer it over beam through because it doesn't require both sender and receiver wired) or limit switch with longer lever or whisker.

if this interferes with volume, make 2 or more corridors side by side but must have something (like shown green rollers) at begin of corridor walls so coconuts don't jam.
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Old February 13th, 2009, 04:30 PM   #10
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I think Panic Mode has it pretty close.

However, I have a few suggestions...

First, I would definitely use a sender/receiver setup. They should be mounted at an angle so that coconut hairs won't tend to cover the device on the lower side. You might also include a small air jet to keep the lower lense clear of hair dust.

I agree that there would be a tendancy to jam, especially considering the friction associated with the coconut hair, further aggrevated by the driving force of the belt. I can see where two coconuts could be lodged into each other and not be inclined to become unlodged... even with free rolling rollers, as Panic described.

I would suggest that the rollers all be driven in the same direction. Consider the rollers from left to right as #1, #2, #3 and #4. All rollers are driven clockwise.

The left chute uses rollers #1 and #2.
The middle chute uses rollers #2 and #3.
The right chute uses rollers #3 and #4.

On the left chute:
Roller #1 tends to drive a coconut into the left chute.
Roller #2 tends to drive a coconut out of the chute.

On the middle chute:
Roller #2 tends to drive a coconut into the middle chute.
Roller #3 tends to drive a coconut out of the chute.

On the right chute:
Roller #3 tends to drive a coconut into the right chute.
Roller #4 tends to drive a coconut out of the chute.

I think that even if the staging area, the area just before the chutes, is filled with coconuts that the setup I described would work as far as passing coconuts into the various chutes without jamming.

I'm still concerned about the idea of separation between coconuts so that an accurate count can be made. I'm assuming that there is a minimum size of coconut... small ones should be sorted out at some point before this part of the process.

Consider this (this is a very rough idea that needs more work)...
Looking at Panic Mode's drawing as displayed on the screen, at a point just after the entry to the chute (the distance should be at least as large as two coconuts end-to-end) and well before the photo-eyes, visualize a paddle arragement that looks like an inverted "T". Looking from above, the depth of the paddle should be about as deep as the diameter of an average coconut. The paddle is to be mounted in the center of the chute on a pivot that goes down through the common point of the horizontal and vertical parts of the "T".

In general, the vertical part of the inverted "T" leans to the left or the right. If the "T" is leaning left, then as a coconut comes to the "T" the coconut hits the right side of the cross bar (the horizontal part of the "T") and passes through on the right side of the "T". Meanwhile, the "T" is driven to lean to the right as the coconut passes through. The following coconut acts similarly but this time the coconut passes on the left and drives the "T" to lean to the left. (Concern: There might be a race-condition between the right and left side.)

This should impose a reasonably reliable gap between the coconuts thus making it easier to count them.

Now... it seems that the geometry of the chute needs to be configured somewhat to accommodate the geometry of the "T" toggle. The chutes probably need to fan-out a bit... but not so much that the photo-eye would miss a count... hmmm...

A thought just occurred to me... if the "T" paddles can operate reliably then maybe you don't need the eyes at all! Maybe the "T" toggle actions can be counted...?
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Old February 13th, 2009, 09:04 PM   #11
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If you have to let them go down the conveyor bunched I think a cognex or similar camera can do it.
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Old February 13th, 2009, 09:33 PM   #12
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I think a simpler sollution would be to use 2 conveyors. The first conveyor is wide and has diverters that taper down to a width only wide enough for the widest coconut. At the end of this converyor there is another conveyor of the same narrow width that is running faster than the first. This will create a gap between the coconuts allowing them to be counted using a thru-beam on a delay. You can also add flights on the second conveyor,this will help.

Last edited by ATU; February 13th, 2009 at 09:36 PM.
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Old February 14th, 2009, 12:46 AM   #13
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Design yourself a conveyor that will merge all the coconuts into a straight line this will be conveyor #1. Put an additional conveyor in line with this one running at a higher rate of speed with a rough top on it to pull a gap between the transfer from one CV to the next of the coconuts. Install a PE with a reflector to cut down on the hair issue. If this doesn’t work for you use the one Panic Mode suggested.
The idea by Panic Mode will work likes a charm on sorter all over the world. You can put a solenoid on it controlled by a PE before the infeed to watch for backups and jams. To control this table top CV. I have used this same setup many times and it works like a pro.
Either one of these ideas will get you running.
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Old February 14th, 2009, 12:52 AM   #14
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you all scared him away
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Old February 14th, 2009, 01:06 AM   #15
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I reckon so .... I wish I had a job to work on at least I would have have some nuts to sort!
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