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 Posted: Feb 21, 2012 - 01:30 PM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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I have a system similar to below.
my task is develop a system that measure mattress width and length. there is no need to take measurements while conveyor is running. it is ok that stop the conveyor and take measurements.
please suggest few methods for this task. |
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~ Chandana ~
a self learner
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Posted: Feb 21, 2012 - 02:28 PM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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Posted: Feb 21, 2012 - 02:33 PM |
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Joined: Mar 27, 2002
Posts: 18529
Location: Lund, Sweden
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What resolution is required? What accuracy is required?
I.e. a light above the conveyor, and photodiodes in between rollers will give you the length with perhaps 2 " resolution. Likewise, a row of photodiodes in one gap between two rollers could give you the width.
Accuracy of length and width would rely on many factors. One of them is how straight along the conveyor the matress is plaed. If it is placed diagonally then measurements will report longer langth and width. |
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Posted: Feb 21, 2012 - 02:37 PM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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| 0.5mm at least |
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~ Chandana ~
a self learner
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Posted: Feb 21, 2012 - 02:41 PM |
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Joined: Mar 27, 2002
Posts: 18529
Location: Lund, Sweden
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Quote:
0.5mm at least
Resolution or accuracy? |
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Posted: Feb 21, 2012 - 02:50 PM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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there are other few things.
1.mattress is not parallel to conveyer
2.final output is calculate the density of the mattress. therefore currently conveyor is on 4 load cells and act as weighing scale.
a worker takes the W,H & L manually using tape and calculate the density.
calculated out put must 0.1 accuracy |
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~ Chandana ~
a self learner
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Posted: Feb 21, 2012 - 03:10 PM |
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Joined: Apr 16, 2001
Posts: 3522
Location: Phoenix, Arizona
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| You're not going to get an accuracy of .5mm with a tape measure, let alone any kind of optical system. And if you measure the length on one edge and then measure the length on the opposite edge, that won't be within .5mm either. Why do you need such a tight tolerance? |
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Posted: Feb 21, 2012 - 03:14 PM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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| project vendors ask the possibility of 0.5mm accuracy. but 1mm accuracy will ok. |
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~ Chandana ~
a self learner
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Posted: Feb 21, 2012 - 03:22 PM |
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Joined: Nov 11, 2003
Posts: 3853
Location: Chicago Illinois USA
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| Is a mattress itself accurate to 1/2 mm? My initial thought it "no way!" It's going to vary more than that depending where you measure it. |
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Discursive design,
Torby
Some days, it's just not worth chewing through the restraints.
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Posted: Feb 21, 2012 - 03:33 PM |
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Joined: Mar 27, 2002
Posts: 18529
Location: Lund, Sweden
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Quote:
calculated out put must 0.1 accuracy
I still think you are having problems with confusing accuracy and resolution.
Apart from that 0.1 makes no sense at all unless you give a unit. (Is it a resolution of 0.1 kilometers? If so then just report 0 always - unless of-course you make huge mattresses  )
What is the resolution and accuracy today, when the measurements are taken manually? |
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Posted: Feb 21, 2012 - 03:41 PM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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@ JohanEkdahl,
takes least 1mm with tape |
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~ Chandana ~
a self learner
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Posted: Feb 21, 2012 - 04:24 PM |
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Joined: Mar 27, 2002
Posts: 18529
Location: Lund, Sweden
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| Last time: Accuracy or resolution? |
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Posted: Feb 21, 2012 - 08:30 PM |
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Joined: Aug 04, 2002
Posts: 1704
Location: Brisbane, Australia
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Some basic arithmetic?
If output is to be calculated to an accuracy of 0.1 percent to what accuracy do You need to calculate volume?
Similarly to what accuracy do You need to measure the dimensions in order to achieve that calculation of volume?
And lastly to what accuracy does the load cell need to weigh in order to achieve final accuracy? |
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Posted: Feb 21, 2012 - 11:44 PM |
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Joined: Dec 11, 2007
Posts: 6843
Location: Cleveland, OH
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For length and width one might use a camera munted on the ceiling. Then calculate the area by simply counting pixels that are white, against a dark background. In this case it doesn't matter if the mattress is tilted at an angle or not. Since you are after volume you don't really need the length and width, the area will suffice.
I'd probably consider using a CCD sensor such as in flat bed scanners, mounted vertically adjacient to the conveyor belt/rollers, to measure the heigth of the mattress.
With the center bludging up in some, and the ruffled, sewn edge sticking up on others, I'm not sure what the heigth really is.
You could define your own standard and have a robotic arm lower a 1 meter x 1 meter, X kg metal plat on the mattress, and then measure its heigth, (wire length, laser dots separation, ultrasound, etc.).
JC |
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Posted: Feb 21, 2012 - 11:50 PM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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What kind of mattress is sized to 1mm accuracy???
Surely if the fabric fits the frame with no slack everything is good? |
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Posted: Feb 22, 2012 - 12:02 AM |
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Joined: Dec 11, 2007
Posts: 6843
Location: Cleveland, OH
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If it was a water mattress one wouldn't have to measure its desity, you could look it up in a book!
JC |
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Posted: Feb 22, 2012 - 12:17 AM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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hugoboss wrote:
What kind of mattress is sized to 1mm accuracy???
Perhaps one ordered by my old drill sergeant. He knew exactly how a bed should be made. |
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Posted: Feb 22, 2012 - 12:34 AM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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| I might add that you will get much better accuracy measuring the hard edge of the bare frame than the soft and deformable edge of the finished mattress. |
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Posted: Feb 22, 2012 - 01:21 AM |
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Joined: Aug 04, 2002
Posts: 1704
Location: Brisbane, Australia
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If the matras is on the conveyor use photo cell to sense begining and end of bed.
Use a rotary encoder on the conveyor drive and count the encoder pulses .
But that comes after You get real with Your specifications.
So GET REAL |
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Posted: Feb 22, 2012 - 02:25 AM |
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Joined: May 03, 2011
Posts: 169
Location: Sri Lanka
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@ JohanEkdahl,
it is 1mm resolution  |
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~ Chandana ~
a self learner
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