A friend is lending me space in his heated fabrication facility to help me
finish my plant imaging system. There were weeks this winter when it was
-11 degrees Fahrenheit in my garage in the morning and plants simply
don't survive temperatures like that. I built this machine to help agriculture biotech
researchers compare different treatments, such as microbial treatments, applied the
plant in the hope that one of those treatments will help the plant to
produce more food. An experiment will consist of dozens of trays like this one
that can weigh up to 20 pounds depending upon the material that they contain and
if they've been watered, so economics of a system like this are really important. To
help with ergonomics of this machine I made this sliding platform that allows a
technician to lift the tray off, hang it off their ligaments, bring it to a
trolley, pick up a new one, bring it back to the platform. They'll then slide the
platform back into position. A proximity switch detects whether or
not the tray has been returned to position and then they close the door.
The rest of the video is the assembly of this sliding platform with all the
mistakes and all the gotchas that I made. I hope that you learn something
from it and can apply it to your own project. Before making the parts I want
to give an overview of the design. This is the module that I'm making in this
video and it connects to existing extrusions in the frame of the machine
by four screws and t-slot nuts. The two telescoping rails are cradled by right
angle extrusions that also connect the frame of the machine to a steel plate. A
proximity switch and steel target are used to detect when the sliding platform
is in position. An additional right angle extrusion is used on the front to
protect people's fingers from a pinch zone. The steel plate has mounted to it a
handle and four smaller right angle extrusions to help register the tray in
the center of the sliding platform. All the
miscellaneous hardware such as the screws came from McMaster as did the
right angle extrusions, the proximity switch came from Automation Direct.
The telescoping rails and the aluminum extrusion hardware came from Misumi as
did the steel plate. I started by cutting the right angle extrusions to
length and then trimming their width down first on the bandsaw, which just
left a mess, and then finally on the mill. The mill doesn't have sufficient travel
so the extrusion was milled in sections. This actually works better than it may
seem at first. I've milled larger pieces on this PM 25 mill. Iit's just a matter of
can you get the section that you need to work on into position on the mill. All
the holes were simply laid out and then drilled at the drill press. Everything
that's being screwed together has enough play that it doesn't have to be super
precise. Even the telescoping rails have some tolerance for misalignment but if
you're going to pay attention to any particular detail it's that the pair of
telescoping rails are as closely aligned as possible. Since these are full
extension telescoping rails they consist of three sections and have this neat
gravity assisted mechanism for sequencing those sections properly. You
can see the hole I've had to drop the screw down through to attach the rail to
the extrusion. Screws that hold these rails in place are not very big compared
to the bulk of the rest of the hardware. Maybe the right angle extrusion doesn't
have to run the full length of the rail. It's not adding an additional support
but it does protect the rail from dirt and and keeps people's fingers out of it.
The right angle extrusion doesn't have to be as thick either, but it does give
the screws more material to grab a hold. I've made machine similar to this before
and a problem that I'd have with those is people wouldn't get the tray all the
way into position and then I was left with images that were skewed. So for this
machine I wanted to have a proximity switch that detected when the tray was
fully in position and wouldn't let people take images unless the tray was
in position. The proximity switches work better at detecting steel than
aluminum so I had this small piece of steel that I've milled slots into and
contoured after attaching it to an aluminum block by super glue. By using steel as a
target instead of aluminum you can double the distance between the
proximity switch on the target. The proximity switch is held in place with a
couple of jam nuts to give some adjustment. The distance between the
proximity switch and the target is only about half a millimeter for steel and if
using aluminum that ideal distance halves. For the steel top plate all of
the holes can be laid out and drilled by hand. Because the through holes have some
slop to them we don't need the accuracy to justify the time at the mill. The
right angle extrusions can be clamped in the position and then match drilled. As
always, can't overstate how nice it is to have a plan in the form of drawings
before starting a project. To help insure that the technician has the tray centered, I
added these right angle extrusions all the way around that help to register
the tray into the middle of the sliding platform. These small right angle
extrusions are held into place using screws into tapped holes in the steel
plate. Two of the edges are in the fixed position have only round holes while the
other two edges have slots to give some amount of adjustability. Surprisingly, the
dimensions of the greanhouse trays or flats are pretty consistent between
manufacturers. To subdivide a tray there are inserts available. The camera
is behind the machine with the back panel removed. Now I just want to test
fit of the module and see if everything is working. It attaches to the machine by four
screws into aluminum extrusions that are part of the frame. The telescoping
rail is easily disassembled but when reassembling them be careful to not harm
the cage that holds the bearings. It's pretty easy to bend that cage. Not clear
in the video is the amount of rubbing the second place especially when the
sliding platform is loaded. The right angle extrusions have a large inner
radius and that's interfering with the telescoping rails so at the mill I
removed that inner radius. I couldn't use the same setup as before but the
extrusion still needed to be supported on the bottom where milling so I could
only mill about six inches at a time but I got the job done. The need to do this
could have been avoided by moving the telescoping rail away from the corner I
just didn't know this was going to be a problem until I ran into it and I was
trying to keep things pretty tight. The next time I make one of these I'll
probably change the position of the holes and avoid the need for that
milling operation. Final steps are wiring the proximity switch and testing. The PLC
has three inputs that are right here. The first one is an emergency stop, the
second one is the door, and the third one is the sliding tray. There's roughly a
quarter of an inch of travel of the tray while the sensor remains closed. Before
we go, I want to say thank you for taking your time to watch this video, thank you
for being a subscriber, and an extra special thank you to those who contacted
me the last couple months during which I haven't been posting videos. I get pretty
sick in March and during April had to prioritize to be sure that the things
that needed to get done did get done. So until the next video
stay healthy.