Peter Nachtwey
Member
No trivial trains and tunnels this time!
This is an actual problem that was solved about 20 years ago by one of our engineers. The goal is to measure the length of a potato strip rapidly. The potato strips would free fall one at a time vertically and they were oriented vertically before falling. The potato strip would break two very fast photo eyes on the way down through a ‘scanner’ or length grader. There is a top photo eye and a bottom photo eye so the bottom tip of the potato strip would first block the top eye then the bottom eye. The top eye will be unblocked when the top tip of the fry uncovers the top photo eye. The sequencing depends on the distance between the photo eyes and the length of the fries.
I was asked if measuring the length of potato strips could be done. I immediately said yes if the potato strips could be oriented vertically reliably. That was a food handling problem. I was asked how because the speed of the fry is not known since the fry does not free fall until the top tip of the potato strip is released. Longer strips are released with the bottom tip closer to the top photo eye so long strips are not moving as fast since they have less distance to free fall.
I told one of our engineers how I would solve the problem in a general way and then let him solve it. He did. I did not ask how. I knew how I would solve this problem.
There are two very high-speed counters, one for each photo eye. The counter used a many megahertz clock so there was no problem with time resolution. The counter for each photo eye would start counting when the photo eye was blocked and stop counting when the photo eye was unblocked. The counts could be converted to time.
What is the formula for determining the length of the potato strip?
This is not trivial but not that difficult. It will take some scratch paper and head scratching. There are probably a couple of ways of looking at this problem. If the counters are configured to measure the time between blocking the top and then blocking the bottom, and unblocking the top and unblocking the bottom then there is a different formula. I think this second method of measuring the time between the blocking on the top and bottom then the time between unblocking on the top and bottom may be easier.
PM me your solutions, if any.
The reason for measuring the length is that the French fry producers want the length to be about 2.5 to 3.5 inches so they fit in one of those red McDonald’s French fry holders or similar. There were a lot of good reasons for measuring the length of fries this way.
This is an actual problem that was solved about 20 years ago by one of our engineers. The goal is to measure the length of a potato strip rapidly. The potato strips would free fall one at a time vertically and they were oriented vertically before falling. The potato strip would break two very fast photo eyes on the way down through a ‘scanner’ or length grader. There is a top photo eye and a bottom photo eye so the bottom tip of the potato strip would first block the top eye then the bottom eye. The top eye will be unblocked when the top tip of the fry uncovers the top photo eye. The sequencing depends on the distance between the photo eyes and the length of the fries.
I was asked if measuring the length of potato strips could be done. I immediately said yes if the potato strips could be oriented vertically reliably. That was a food handling problem. I was asked how because the speed of the fry is not known since the fry does not free fall until the top tip of the potato strip is released. Longer strips are released with the bottom tip closer to the top photo eye so long strips are not moving as fast since they have less distance to free fall.
I told one of our engineers how I would solve the problem in a general way and then let him solve it. He did. I did not ask how. I knew how I would solve this problem.
There are two very high-speed counters, one for each photo eye. The counter used a many megahertz clock so there was no problem with time resolution. The counter for each photo eye would start counting when the photo eye was blocked and stop counting when the photo eye was unblocked. The counts could be converted to time.
What is the formula for determining the length of the potato strip?
This is not trivial but not that difficult. It will take some scratch paper and head scratching. There are probably a couple of ways of looking at this problem. If the counters are configured to measure the time between blocking the top and then blocking the bottom, and unblocking the top and unblocking the bottom then there is a different formula. I think this second method of measuring the time between the blocking on the top and bottom then the time between unblocking on the top and bottom may be easier.
PM me your solutions, if any.
The reason for measuring the length is that the French fry producers want the length to be about 2.5 to 3.5 inches so they fit in one of those red McDonald’s French fry holders or similar. There were a lot of good reasons for measuring the length of fries this way.
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