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A question of efficiency

This topic is mostly for glenbarnett, who has Math Fu and may be able to make my life easier, if he finds this issue interesting. Of course, everyone can look behind the cut tag, if you care.

Ye Olde Inventory issue

Old Robot Layout:

Both Robots are linear robots. The old Robot has 16 bays. The front of the robot held the return rack (where drugs are put into the robot) and the conveyor belt (where drugs come out of the robot), which were at opposite ends of the robot. The bay on the back wall next to the conveyor was bay 1, and progressed through bay 8 (near the return rack). Then the next bay was bay 9, on the front near the return rack. Bay 16 was next to the conveyor belt. Thus, there is a slight bias on putting drugs on bays 9-16, as they were on the front side of the robot, and this saved a slight amount of time for the robot head not having to rotate 180 degrees.

In addition, bays 9-16 were closely spaced, and bays 1-8 were not. Bays 1-8 were more widely spaced out (due to architectural complexities) and bay 7 was actually opposite bay 9. But I digress.

The old robot was 35 feet long and 9 feet wide. It had 3500 storage inches of space, all accommodating the “small” package size product. This meant that there was no advantage to placing “bulk” or “small” products in any particular location aside from their usage, and that the robot could not accommodate “large” package size products. Each bay was the same size, even though the spacing was not symmetrical on the back wall. Every bay had 49 rods, and each rod was slightly more than 4 inches long.

Bulk products are the smallest, and can go on any rod.
Small products are the medium size, and can go on “Small” or “Large” rods.
Large products are the largest, and can only go on “Large” rods.

New Robot Layout:

The new robot is 30 feet long and 8 feet wide. Despite a smaller footprint, this robot has about 7200 storage inches of space, of all package sizes. The new robot’s rods are 7 inches long. There are 12 bays. Bay 11 is on the front side near the conveyor and bay 7 is on the front side near the return rack (almost but not next to; I'll explain further), and bay 1 is on the back side near the conveyor belt. Bay 6 is the bay furthest from the conveyor, regardless of its location front or back. Bay 12 is actually directly next to the return rack (yes, they’re not in order) and thus the order is 1-6 on the back wall, and 12, 7, 8, 9, 10, 11 on the front wall.

The major difference between the robots, aside from the rod layout, is that there is a second output device above bay 7. Although this loses some storage space, it gains us flexibility. This is a Envelope Delivery System, and will eventually be used for output 24/7. The conveyor belt can put out 700 doses/hour, if used maximally, and is usually only used once daily. The EDS can put out 600 doses per hour, although when used for first doses rather than cartfill, will rarely run that fast.

Bays 1-5 have 104 rods of Bulk size, and 7 rods of Large size.
Bay 6 has 30 rods of Small size, and 28 rods of Large size.
Bay 7 has 52 rods of Bulk size, and 7 rods of Large size.
Bays 8, 9, 10, and 11 are the same as Bay 6.
Bay 12 has 2 rods of Small and 12 rods of Large.

As you can see, inventory management for the new Robot to minimize the Robot head movement from drug to output device is much more difficult than for the old Robot. The only thing I can say with certainty is that Bay 6 is the red-headed step child...but even so, its inventory is very close to the EDS, and it has good storage value in comparison to bay 8 in the old Robot. Stocking bay 8 in the old Robot meant that the Robot head actually had to move AWAY from the conveyor belt in order to stock it. Interesting, eh?


( 7 comments — Leave a comment )
Feb. 14th, 2004 10:09 pm (UTC)
Hi Seth. Sorry, I've been sick a few days.

I don't actually see a problem described here, only a comparison between your new and old layout, of which I understood perhaps half.

Additionally, were there to be an actual question there (other than the rhetorical though admittedly true, 'Interesting, eh?'), it doesn't look to me like there'd be enough information to answer it, whatever it might be.

1) What is it you want to do?

2) Let's address some of my ignorance and potential misunderstandings:

I gathered from careful re-reading that your pharmacy has a robot that can take stock (drugs and such) that you put into it and dispense it later. Presumably it moves around the hospital and dispenses stuff when you tell it.

- Both Robots are linear robots.

What does that actually mean? Assume (correctly, as it turns out) that I know almost nothing whatever about industrial robotics.

My first guess (no, to be honest, it's my third guess - I eventually figured out I had misunderstood a couple of times) is that you mean that the part inside the robot that takes the drugs from wherever it keeps them to where it dispenses them moves along in a straight line.

- The old Robot has 16 bays.

A bay is a storage area in the robot for putting drugs into?

Can it only hold one kind of drug at a time?

More questions later.

On reflection, it's beginning to look like your question is something like "Which bays in the new robot will be the ones I should prefer to use to minimise head movement?"

Feb. 15th, 2004 01:38 am (UTC)
When I first read Seth's post, I too, wondered where the question came in. However, my second thought was, "gee, wouldn't it be better if we just called Glen so that Seth could explain it all at once?" So I propose that Seth and I figure out when a good time to call you is (I still have no grasp of what time it is in Australia at any given moment...Japan is 14 hours ahead of us. Are you too? or are you more?) Anywho, we don't do nearly enough to support our long distance carrier, so we really ought to just give you a call!
Feb. 15th, 2004 02:47 am (UTC)
Industrial Robotics
Sorry you've been sick. This was not any question that was under any time pressure for anyone. It's a question of inventory efficiency for maximal speed in medication cart preparation.

I knew when I was writing it that I wasn't explaining myself with perfect clarity. Nevertheless, since I had my paperwork handy, I wanted to put down what I could before I got tied up in something else.

This robot is an inventory device. It moves back and forth on a track in a straight line (thus it is a linear model) as opposed to a stationary model that rotates in place. The robot pulls drugs off of bays (or racks) that are laid out in two straight rows; the circular model pulls drugs off bays at the edge of the circle.

The inventory in question are drugs, which are unit dose packages that are packaged to hang on rods. Each bay (or rack) has a variable number of rods, due to size of the package and size of the bay. Each rod only holds one type of drug. The closer the bay is to an output device (either the conveyor belt or the Envelope Delivery System), the faster that medication can get from inside the robot to a human who can take it to a patient. The robot has a maximal speed that it can operate at, which it usually is operating at; thus, the way to speed up inventory delivery is to maximize the placement within the robot.

Basically, it's a big box, 30' long, with two racks running down the length. I gave you the locations of the racks within the box and the location of the output devices; if you would actually like a picture or diagram, I can provide it.

The box actually contains the robot, and the robot only moves within the box. It does not move around the hospital...it is not designed to do so. We're actually testing a different robot that makes deliveries, but that one has serious technical difficulties functioning in the RF mess that is your modern hospital.

Now that I typed all of that, Karen recommended that we actually speak. That sounds like a marvelous idea, not the least of which that we haven't done so recently. Perhaps we should implement such a conversation?
Feb. 16th, 2004 01:27 am (UTC)
Conversation conservation

As much as I'd like to chat, for the moment text is better. It allows me to keep rereading it as I begin to digest the problem, and means I don't have to try to scribble down details.

(Added to that I can't speak for more than a couple of minutes without coughing a lot right now.)

At some point a phone call would probably be a good idea. The schedule will probably work out best if we talk early evening your time/late morning my time, but we'll get to that later I think.

I think I now have the basic circumstance clear.

If you have diagrams in electronic form, I would happily look, but its not particularly necessary I think.
Feb. 16th, 2004 10:25 am (UTC)
Re: Conversation conservation
Sorry to hear about the coughing. Here's hoping you're fond of hot tea with lemon and honey. :)

Early evening is doable for a conversation. We might even get to business before late evening!

I hope you have the basic circumstance clear. Hell, I hope I do as well! It'd be nice to be able to do my job...

...and I shall see if any of the relevent documents remain in PDF at work. If so, you'll get them via email. Easier than posting them.
Feb. 15th, 2004 06:17 am (UTC)
Either I'm gettin' more forgetful or school is taking its toll....
No, this has nothing to do with robots. (though I hereby suggest you name your new robot "Servo.")

I can't believe I forgot your birthday! I hope it was a very happy one, my ever-so-slightly older friend!

(Belated is better than completely forgetting, right? Right?)
Feb. 15th, 2004 10:43 am (UTC)
Re: Either I'm gettin' more forgetful or school is taking its toll....
I thought madness was supposed to take its toll...?

Hmm..."Servo" does have a nice ring. I suspect that in my department, I would be one of two geeks who would get the joke. But I'll push for it.

I can believe you forgot my birthday. It's no big thing. I had a good birthday, and it's been a good month overall. Belated is fine, sure.

For example, there are some friends of mine (not that I would name names) who have birthdays as close to mine as two weeks, and still don't remember mine. I don't hold that against them. I often forget birthdays, so I can't call that particular kettle black. I won't detail the important ones I've forgotten recently (cough! Dad! cough!) but needless to say, I will hold nothing against you on this topic. Or others.

And if you're reading this, and it's your birthday, happy darn birthday!
( 7 comments — Leave a comment )