A Funny Design Story: The Amazing Marker Cannon
In the early days of working with NAS (a packaging equipment manufacturer) we used to do a lot of work for Avery Dennison. One of the first jobs we did together was to build a machine that processed magic markers straight off the assembly line and packaged them in individual clamshell packages. We started out with a cleated conveyor feeding markers out of a hopper into an orienting mechanism which aligned the markers end to end. They then fed into a tube which then used a pneumatic escapement to stack the oriented markers side by side.
The general idea was to use a large blower to send the markers up an array of tubes onto a tray with guides which would then escape the markers individually into the clamshells. To test the theory we bought a 1 hp blower and made a chamber to place the marker into. We connected a piece of flexible PVC to the chamber and fired up the blower.
It was amazing! The marker shot out of the end of the tube, all the way across the shop and shattered against the back wall! After putting a small damper in the tube we were able to control the force and trajectory of the markers and considered the experiment a success. The next step was to put five tubes side by side and connect them to a manifold where we would stack the markers to achieve the desired rate for the machine. From the description so far can you guess the result? Think about it for a bit, no fair looking…….
Ok, can you picture it? We had five markers all stacked up in the manifold, the tubes fed out and up to the tray and we turned on the blower, and…. the markers all left the manifold and started their journey up the tubes! One marker flew out of a tube and as you may have guessed, the other four slid back down the tubes and into the manifold. This was a great lesson in resistance that we should have been able to anticipate. As soon as one tube was clear, that was where all of the air went.
It was easy to see in hindsight that the blower wouldn’t work for separate tubes no matter what we did; we would need to use multiple blowers. As it turned out we ended up using a rubber wheel to “pump” the markers up a pair of tubes, lined the markers up side by side on the tray and pushed them up the five tray lanes and into the clamshells. This just emphasizes that trying to poke as many holes as possible in the design concept can’t hurt and that there is no substitute for experience. This can also help explain where all those spare parts that litter every machine builder’s shop come from!