What would be the best CPT expression so that if I wanted to put something on a belt every say 7'. The belt runs on a VFD with a top speed at 500 FPM. I can't figure out the correct equations so that it will load every 7'. I know this has to be easy, just can't get my head around it. Thanks for the help!
Gapping
- Thread starter mae
- Start date
Without knowing your application here is what I would do to keep it simple. Install a prox (to sense a bolt/screw head) on the drive sprocket of the conveyor and count the pulses for every 7' of belt travel. Put the counted pulses as a counter preset. Use the counter .DN bit and load your object on the conveyor. Reset the counter after loading the object so the counter starts cycle again.
OkiePC
Lifetime Supporting Member
Even simpler:
Convert your formula for belt position into the units needed by your PLC, and test for accuracy throughout the speed range with a hand held tach. if you add feedback, my preference is a tailshaft driven resolver (AMCI HT-20). Don't mess around with sticking inductive sensors near a sprocket, it's a headache...open loop belt control and velocity commands are usually close enough for material handling applications. Calibrate your control to the hand tach, and linearize the slope at two points. Should never have to be adjusted unless a reducer ratio is changed, but it's a good idea to re-tach it after even a motor changeout. Modern sensorless vector drives can do an outstanding job of matching velocity control then it's just D=vt...
If you are commanding the speed of the belt, and can monitor product entry and/or exit into a PLC array, you can paint a literal histogram of it's contents...
I usually set a range for the belt length to a value larger than what is physically possible and set up a rolling queue. Set a range (LIM) check upper and lower value at your desired Distance interval, then calculate for rollover. When your LIM block goes true, the action is triggered. If you can monitor actual feedback go bi directional...In a Logix5k controller, I would use a periodic task running faster than hello for max. precision.
Convert your formula for belt position into the units needed by your PLC, and test for accuracy throughout the speed range with a hand held tach. if you add feedback, my preference is a tailshaft driven resolver (AMCI HT-20). Don't mess around with sticking inductive sensors near a sprocket, it's a headache...open loop belt control and velocity commands are usually close enough for material handling applications. Calibrate your control to the hand tach, and linearize the slope at two points. Should never have to be adjusted unless a reducer ratio is changed, but it's a good idea to re-tach it after even a motor changeout. Modern sensorless vector drives can do an outstanding job of matching velocity control then it's just D=vt...
If you are commanding the speed of the belt, and can monitor product entry and/or exit into a PLC array, you can paint a literal histogram of it's contents...
I usually set a range for the belt length to a value larger than what is physically possible and set up a rolling queue. Set a range (LIM) check upper and lower value at your desired Distance interval, then calculate for rollover. When your LIM block goes true, the action is triggered. If you can monitor actual feedback go bi directional...In a Logix5k controller, I would use a periodic task running faster than hello for max. precision.
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500 fpm = (500*12)/60 inches per second = 100 ips
To do something every 7 inches, you need to do it every 7/100 seconds, or every 70 mS
so the formula is...
Trigger time (in Seconds) = Inches_Separation/((fpm*12)/60)
Or simplifying,,,
= Inches_Separation/(fpm/5)
To do something every 7 inches, you need to do it every 7/100 seconds, or every 70 mS
so the formula is...
Trigger time (in Seconds) = Inches_Separation/((fpm*12)/60)
Or simplifying,,,
= Inches_Separation/(fpm/5)
Mickey
Lifetime Supporting Member
Isn't 7 feet?
60/(speed of belt in FPM/7)= sec per put something on belt
60/(500/7)=.84 sec.
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sorry, my bad (eyesight in this case) - i read 7' as 7" - doh!!
revised....
500 fpm = (500/60 feet per second = 8.33333333 fps
To do something every 7 feet, you need to do it every 7/8.3333333 seconds, or every 840 mS
so the formula is...
Trigger time (in Seconds) = Feet_Separation/(fpm/60) = 0.84
revised....
500 fpm = (500/60 feet per second = 8.33333333 fps
To do something every 7 feet, you need to do it every 7/8.3333333 seconds, or every 840 mS
so the formula is...
Trigger time (in Seconds) = Feet_Separation/(fpm/60) = 0.84
Mickey
Lifetime Supporting Member
That would give you..
(500/60)*7=58.33
That is not the same as daba's.
But "60/Actual Speed (FPM)*7" will give you the same results.
(60/500)*7=.84
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