timing calculation

plcnewbie

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Jan 2005
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I need help with a timing calculation.
I have a gate x long which should open based on when a product of x length is clear of it so as not to get squashed during the transition. The speed of the line is variable and I also need to close the gate so product does not run into the rail halfway through. I am using a sensor to detect the product rise and falling edges. Can someone help me with a formula for this calculation please. I am having great touble thinking of it.

Thanks
 
Where to begin? Do you have a know distance between products? How are you monitoring the speed of the line? Is the product length a know value or variable?



plcnewbie said:
I need help with a timing calculation.
I have a gate x long which should open based on when a product of x length is clear of it so as not to get squashed during the transition. The speed of the line is variable and I also need to close the gate so product does not run into the rail halfway through. I am using a sensor to detect the product rise and falling edges. Can someone help me with a formula for this calculation please. I am having great touble thinking of it.

Thanks
Click to expand...
 
Presumably you know the distance from the sensor to the gate. The time for the product to reach the gate is that distance divided by the speed of the product. If the gate is in the wrong position, that's the amount of time you have to get the gate moved to the right position once you detect the leading edge of the product. Its also the amount of time you need to wait before moving the gate after you detect the trailing edge.

Example: Line speed is 100 FPM, sensor is 6 inches from gate. It will take 0.3 seconds for the leading edge of the product to travel from the sensor to the gate. At 500 FPM it will take 0.06 seconds.
 
dskohio said:
Where to begin? Do you have a know distance between products? How are you monitoring the speed of the line? Is the product length a know value or variable?
Click to expand...


product length will be known based on the cut length, speed of line is going to be read from a pflex drive, and converted to speed from hz. Distance between products can vary but at full speed should remain basically the same.
 
Newbie,

Here are some equations taht calculate the Product Speed based on your sensor AND Product Length, which you say you know.. Sensor should be located close to gate. This has advantage that Speed is not dependant on belt or product slippage.

Variable definitions:

D = Distance to Gate (INCHES)
Tle = Time that Product Leading Edge is detected (SECONDS)
Tte = Time that Product Trailing Edge is detected (SECONDS)
Tgo = Time to Open Gate (SECONDS)
L = Product Cut Length (INCHES)
PS = Product Speed (SECONDS)

PS = L/(Tte-Tle) ;(Tte-Tle must not be 0)
Tgo = Tle + (PS/D)

Tgo must be enough time to get gate open. If not, you must move the sensor farther upstream from the gate.
 
Last edited:
What exactly are the constraints on moving the gate? Does it have to move during the gap between products?

My experience with similar applications has been in switching between two collection points for cut sheets of paper. When hopper A is full, the diversion gate shifts and directs the paper to hopper B. Hopper A gets emptied while hopper B is filling. When hopper B is full the gate shifts back to direct the paper to hopper A.

In that application, for each cycle of product + gap, there is a window where it is permissible to shift the gate. The beginning of that window is when the leading edge has passed the gate by some distance. The end of the window is when there is not enough time to shift the gate before the leading edge reaches it. I just had to make sure that the gate could only be shifted within that window.

One additional thing I had to do was to adjust that window based on line speed. The gate always takes the same amount of time to shift, but that time represents a different amount of product travel at different speeds.
 
Steve Bailey said:
What exactly are the constraints on moving the gate? Does it have to move during the gap between products?

My experience with similar applications has been in switching between two collection points for cut sheets of paper. When hopper A is full, the diversion gate shifts and directs the paper to hopper B. Hopper A gets emptied while hopper B is filling. When hopper B is full the gate shifts back to direct the paper to hopper A.

In that application, for each cycle of product + gap, there is a window where it is permissible to shift the gate. The beginning of that window is when the leading edge has passed the gate by some distance. The end of the window is when there is not enough time to shift the gate before the leading edge reaches it. I just had to make sure that the gate could only be shifted within that window.

One additional thing I had to do was to adjust that window based on line speed. The gate always takes the same amount of time to shift, but that time represents a different amount of product travel at different speeds.
Click to expand...

yes it needs to change between products and back between products.
 

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