Vertical Lift

Sorry if this is in the wrong spot, but I'm fairly new to this. I'm trying to design a small tray that will be able to move vertically
along a CD rack for a retrieval system. I'm probably going to be using an empty shell of a CD drive for in/out movement in grabbing the CD from the appropriate slot. If I have to I can make my own tray, that's not really an issue.
I've been thinking about the best way to accomplish the vertical movement and I don't know a lot about leadscrews, wormgears etc. I've been looking at a lot of stuff online (most of it patent junk) and while I have a general idea of how these things work I would like some clarification.
The device itself will not be heavy and the load (a CD) is not heavy either. Would a leadscrew setup and guide rails along the side be a good way to go about this? I like the wormgear idea as it would essentially lock the tray in position once it reaches its destination, at least from what I've read. The device will be powered by electric motors, perhaps a stepper motor. Am I on the right track?
Thanks for any input.
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Assuming cost is a driving factor: A lead screw (3' of all-thread) attached to an OLD floppy drive stepper motor is the way to go. OLD floppy drives used a stepper to move the heads. The factory "screw" mechanism can be removed, and yours attached.
I would use a steel bar, maybe 1/4" by 2" to guide the little pickup vehicle, using plastic guides for stabilization.
I assume you want this to be stand alone, so you are going to need a processor to control the motor. A Texas Instruments 430 processor is worth a look. The development system, including processor, C language and assembler, all that's needed to write, program and make a working embedded processor is only $20. (eZ430-F2013) http://www.ti.com/corp/docs/landing/ez430tool/index.htm?DCMPC0Day&HQS=Other+OT+ez430
Good Luck, DJ

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Hoov wrote:

Free advice worth everything it cost: consider a servo motor of some type. A lead screw seems like overkill for something so light. Of course, if the CDs are accessible to people, pets, dropped items, etc., then light can become heavy in a hurry.
Bill
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Some of the old floppy drives used a neat arrangement with a stainless foil "belt" wrapped around the stepper pulley then fixed to the carriage. For a one off the belt could be cut by hand.
Grab some old printers and maybe one of those CD storage gadjets and have a look inside. Have fun.
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A stepper motor and timing belt is the way to go for the drive system. For guides, check out Misumi, USA's automation components catalog. (http://www.misumiusa.com iirc). You can get some 8 mm linear bearings for about #$12-$16 each, and the rods for them aren't that much more.
--
Anthony

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Hmm, I do have an ancient floppy drive in my PC that I never use anymore. Might be time to finally junk the thing.
I did actually order a busted wide format printer from ebay to use for parts. I know at the very least the metal rod inside could be used for a guide rail, and it should be approximately 13" in height. The CD rack I ordered is 17", but that can be cut down to size easily.
As for the microprocessor, I'm using the Parallax Propeller. My buddy used it for his color sorting project so it won't cost me a dime. Thing is pretty sweet though, runs on 3.3V DC, has 8 32-bit cores with shared memory and can be programmed in straight assembly (bleh) or its own Spin low-level (assembly) language.
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    --If space isn't a problem and you really want to lowball the price you can do without the linear bearings by making a 4-bar link (?), a la Watt's parallel motion; i.e. something like one of those draftsman's desk lamp but with a platform replacing the lamp.
--
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When I was building prototype inkjet plotters the mechanical engineer used a stepper with a pulley and a polyester cord (crab line) or fine steel cable to drive the head, which ran vertically and probably weighed more than a CD tray needs to. It ran open loop with an optical Home flag, but didn't need to move very fast so skipped steps wasn't an issue. I could slew it as rapidly as the motor could handle by ramping up the step rate.
If the motor and idler pulleys are rigidly mounted and the cord doesn't stretch, overshoot and oscillation shouldn't be much of a problem. You can observe it on an oscilloscope by watching the output of a small solar cell whose illumination is partially blocked by the carriage.
The vertical guide rails could be standard extruded aluminum stock with skateboard ball bearing guides on the carriage. Sand the contact surfaces flat using fine sandpaper around a smooth metal block.
Jim Wilkins
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