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General purpose cd/dvd gripper

actuator cd changer cd duplicator cd rack dvd dvd duplicator gripper jukebox robot actuator robotics robotic_gripper SCARA

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I'm trying to design an open source robot actuator for gripping CD discs.
The main applications I have in mind are either a disc duplicator robot and a jukebox/cd changer.

Design constraints:
1) Needs to grip the disc edges, not center hole, so it can be used with cd spindle.
2) As slim a profile as possible to maximize the number of discs a jukebox rack could hold.

Below is a rough model of what I'm thinking. As you can see, I'm still undecided about the best method for servo attachment.

Any feedback or design suggestions?

The size, shape and location of the hole in the center of the disc is standardized, and discs must adhere to that standard in order to work in most optical drives. The size & shape of the outer parameter are variable. In theory there are only three "normal" sizes, but in practice there are "normal" CD/DVD discs, mini discs (aka CD singles), business-card CDs etc.

Other advantages of grabbing the disc from the middle include:

  • A simple 2-point-of-contact gripper can be made with a $7 RC servo, two 3D-printed parts and small spring (which may also be 3D printed in ABS). The design is fairly self-explanatory: you just need a 2-jaw gripper that expands (due to the force of the spring) to grip a disc, and can be released by using the servo to compress the spring. You could do it the other way around, but this approach is more tolerant of variations in the size of the center-hole.

  • It is possible to grip the disc from the center while inserting it into a tray or slot-loading optical drive (the first option being the easiest to handle). I don't think either of those drive designs would be compatible with the gripper in your images.

  • When moving a disc, the disc center (which you normally need to know in order to position a disc properly) is always in an exact known position relative to the end effector. If you grab the disc by the outside edge, the center position will vary depending on the disc shape and diameter.

As far as using it with a CD-spindle goes: Find a rotary tool or jigsaw, cut yourself a roughly 7" wide disc of scrap wood (or whatever) and attach three lengths of wooden dowel (or any smooth rods really) approximating an equilateral triangle, spaced to hold a stack of discs in place. It shouldn't take more than a few seconds to take a stack of optical discs off a spindle and set them in this rack, and it will save you a lot of trouble when interacting with optical drives.

Are you sure you coudnt get away with gripping it from "the sides", plier-style? that way you would avoid a couple of joints and therefore eliminate a lot of sloppiness, which in turn needs more space horizontally (if we're talking 3d printed that is)...