Box reject without shift register and 1 input!

[Mrclk 0]

Ok, here I go again: I have a project in hand which consists of rejecting a box with open flaps off a conveyor belt. I have a roller conveyor on one side of the case conveyor and a pneumatic pusher on the other side. We have no encoder on the case conveyor so shift register is not duable unless it becames absolutely necessary. I spoke to a colleague and he suggested using a photoeye looking down at the box and tieing it ito a counter and also a greater than function. The case conveyor runs at a constant speed of 140 feet a minute. So he recommended to measure the leght of the box in time. Based on this measurement set source B on the greater than function, you know just a little bit longer than a closed box(box flaps are about 2.5 inches deep) whenever an open box goes by it will be about five inches longer and therefore trigger the photoeye for a few more miliseconds. When the value from the photoeye-triggered timer exceeds this value we would have a reject. After this we would have another timer giving us a delay before the box gets kicked out(I might do away from this by setting the delay mechanically via moving the photoeye closer to the air cylinder) and another off delay to hold the cylinder out long enough to push the box out. My problem is, I only have one input(which I will use for the photo eye)available on the 16 terminal input flex I/O module; therefore, in order to reset all those timers back to zero I woul have to use internal logic and this I am not very familiar with. I was wondering if this is actually duable and hoping someone could give me some input on this matter. Thanks in advance.

[Sergei Troizky 26]

Use two sensors in cascade connection in the reject area. Adjust distance between them so that both sensors active means box oversize (flap open or no gap between boxes). On such signal activate your reject. Edited 27 Nov 2006 by Sergei Troizky

[Ken Moore 23]

Well.... Shouldn't need any resets if you use standard non-retentive timers. Just three cascading timers. When the box flap PE timer times out, the done bit from that timer, will start the delay timer, when the delay timer is done, fire the pusher until timer three is done. I threw the attached ladder together really quick, it is untested, and may or may not work. PE_PUSH.pdf

[Mrclk 0]

Thanks I will finish installing the hardware and try this logic as soon as I can.

[Ken Moore 23]

You will have to come up with your own timer presets. I just threw in some numbers so the program would compile. Once you try the code, if you have any problems, post back with specific questions. Someone can probably help. If you do experience difficulties, please post your code, if not the entire file, then at least a snap shot. It helps a lot and we don't have to play twenty questions. You may want to explore the two sensors in series as well, that way you won't have to use trial and error for the "bad" timer preset.

[Mrclk 0]

This is a very good approach; the only problem is, the gaps between boxes sometimes are shorter than the box lenght. This would trigger both photoeyes not only by the open flaps but also by two boxes close together. Unless there is a different aproach to the logic. Something like a latch that would get engaged by the leading edge of the box and disengaged by the trailing edge to avoid counting two boxes as one. Any toughts?

[Sergei Troizky 26]

I would simply add sensors to the cascade chain, between the mentioned ones, to detect possible gap. If they are evenly distributed with the pitch less than the minimum gap betwen boxes, then again the cascade being on will mean box oversize (without gaps, meaning a single box). Without detailed analysis, I speculate N+1 sensors are necessary for minimum gap of 1/N of the box size. Edited 28 Nov 2006 by Sergei Troizky

[Mrclk 0]

The logic actually works. After I finished installing the hardware and put the logic together it took me a while to get the timing in zinc with the product. I still have to tie the logic into a button on a touch screen to turn the process on and off. attached is a screen shot of what I have so far.

[Ken Moore 23]

Thanks for following up and letting us know how it turned out. You should be able to add an XIC or XIO to the pusher extend logic. When the panel changes it's state, the rest of the logic will still be functional, but the pusher will not extend. If you are feeling ambitious, you could also add a counter that counts the number of rejects in a given time period. Might come in handy later, when management wants to know what the reject rate is.