The idea of having a brake, or clamp, to establish and control gap size is a good idea.
Here is a possible flow regulator based on one that I developed many years ago. The purpose was to ensure a minimum gap size. It didn't matter if the gap was big, but it did matter if the gap was too small or non-existent. The following is based on the worst-case condition of no gaps between items as they enter the flow regulator area.
EYE-A:
When Eye-A goes from OFF to ON, the program knows that a box has just entered the push-area. However, it is not yet in position to be pushed. The pusher routine arms the Clamp and then checks the current color-marker to determine the appropriate course of action.
- If the current color-marker IS Red then the pusher knows that it needs to push this box... but not yet.
- The Red Pusher Routine sets the "PUSH" flag.
- If the current color-marker IS NOT Red then the Red Pusher Routine sets the "PASS" flag.
- The Red Pusher Routine knows it needs to let the box pass and pass on the color-marker... but not yet.
EYE-B:
If the Clamp is armed, and if Eye-B is ON, then the Clamp is closed until the Clamp is dis-armed.
If the Clamp is dis-armed, then, regardless of the state of Eye-B, the Clamp is opened.
(There is an excetion listed near the bottom of this post.)
EYE-C:
If the
"PUSH" flag is set, then when Eye-C goes from ON to OFF, the box is pushed. After the pusher extends and then is fully retracted (at home), the routine discards the current color-marker, dis-arms the Clamp and resets the "PUSH" flag. If the Clamp was holding a box then the box is released and allowed to move toward Eye-A in the pusher area
If the
"PASS" flag is set, then when Eye-C goes from ON to OFF, the box is allowed to pass through the pusher area.
The GAP:
If the
"PASS" flag is set, then the size of the gap can be as minimal as the distance between Eye-B and Eye-C, or as extreme as "infinitly large".
- Option-1: At Eye-C OFF, dis-arm Clamp (gap = minimum)
- Option-2: At Eye-C OFF, run a timer then dis-arm Clamp (gap = variable, greater than minimum)
- Option-3: At Eye-A OFF, dis-arm Clamp (gap = box-size)
- Option-4: At Eye-A OFF, run a timer then dis-arm Clamp (gap = variable, greater than box-size)
In any case,
DO NOT reset the
"PASS" flag until Eye-A goes OFF. Then, at that time, remove the color-marker from the first queue and deposit it into the second queue.
If the
"PUSH" flag is set, then execute the "push" when Eye-C goes OFF (gap = minimum)
In Figure-1 (below), the first box enters the clamp area. Notice that there are no other boxes ahead of the box at Eye-B. Unless the process requires a gap-size larger than the size of a box, it should be quite evident that there is sufficient gap ahead of the leading box. This means that on start-up, as long as the pusher area is clear, the clamp will always allow the first box to pass into the pusher area toward Eye-A.
FIGURE-1
In Figure-2 (below), the leading box trips Eye-A. That is, the eye transitions from OFF to ON. Two things happen at that point.
1. The Red Pusher Routine checks the current color-marker in the queue.
- If the current color-marker IS Red then the pusher knows that it needs to push this box... but not yet.
- The Red Pusher Routine sets the "PUSH" flag.
- If the current color-marker IS NOT Red then the Red Pusher Routine sets the "PASS" flag.
- The Red Pusher Routine knows it needs to let the box pass and pass on the color-marker... but not yet.
2. The Red Pusher Routine "Arms" the Clamp. (Eye-A going from OFF to ON causes the Clamp to be "armed".)
Notice that there is no gap between the first and second box.
FIGURE-2
Figure-3 (below) shows that, since the Clamp was armed by Eye-A going ON, the Clamp is closed on the following box. Meanwhile the first box continues moving forward.
FIGURE-3
Figure-4 (below) shows that a "minimum gap has been established. In this case, the color-marker associated with this box happened to match the pusher color, thus calling for a "push". When the pusher returns to home, the Clamp is dis-armed and the next box is allowed to move toward Eye-A in the pusher area.
FIGURE-4
It would be wise to address those cases when the line is restarted with boxes in the line. In that case, there might be a box in front of Eye-A. Depending on your code, you might, or might not, have retained the status of that box when the line was stopped. It could be that the conveyor "coasted" a bit, bringing the box to Eye-A. If the pusher routine was not "running" because the line was stopped then you might not "catch" Eye-A going from OFF to ON. Be mindful of these kinds of "gotchas"... they must be addressed if you want the process to be flawless.
You might want to set it up so that the Clamp always closes when the process
or is ON but the process is not running. That is, you probably don't want to have the Clamp "plumbed" to be Normally Closed. If you did have the Clamp "plumbed" Normally Closed then you might have to turn off the air supply before you can remove a box from the Clamp.
Whether or not you need to have a Clamp at each Pusher Station depends on the reliability of the transport conveyor. That is, if it is possible that the boxes might "gang-up" between stations then you probably should have local Clamps at each station.
Otherwise... well, you know your system better than I do... so, it's your call!
(820)