Fused Deposition Modeling (FDM), also known as Fused Filament Fabrication (FFF), is one of the most popular and widely used 3D printing technologies. FDM printers use a thermoplastic filament which is heated and extruded through a nozzle, layer by layer, to build an object. There are variations and advancements in the FDM design and mechanism. Here are some of the different types and their explanations:

1. Cartesian FDM Printers:

   • The most common type of FDM printer.

   • Uses a Cartesian coordinate system (X, Y, Z axes).

   • Movement is typically achieved through belts, rods, and lead screws.

   • Examples: Makerbot Replicator, Creality Ender 3, Prusa i3.

2. Delta FDM Printers:

   • Uses three arms in a triangular configuration to control the position of the nozzle.

   • It operates in a cylindrical volume rather than the rectangular volume of Cartesian printers.

   • Can be faster and more precise in some instances, but may have a steeper learning curve for users.

   • Examples: AnyCubic Kossel, Monoprice Mini Delta.

3. CoreXY FDM Printers:

   • A specific type of Cartesian printer that uses a unique belt arrangement for movement in the X and Y axes.

   • Known for precise and fast movements because of the way the motors work together to achieve motion.

   • Examples: Voron, Hypercube Evolution.

4. Polar FDM Printers:

   • Uses a polar coordinate system with a rotating bed and a moving arm.

   • Offers potentially faster print speeds but is less common in the consumer market.

   • Example: Sculpto 3D.

5. Belt (or Infinite Z) FDM Printers:

   • Features a conveyor belt as the print bed.

   • Allows for theoretically "infinite" printing in the direction of the belt, ideal for very long parts or continuous batch production.

   • Examples: Creality CR-30, Prusa i3 with a belt mod.

6. Multi-material and Multi-extruder FDM Printers:

   • Equipped with multiple extruders or a multi-material upgrade.

   • Capable of printing objects with multiple colors or materials without changing the filament manually.

   • Examples: Prusa i3 MK3S with MMU2S, BCN3D Sigma.

7. Hanging/Robotic Arm FDM Printers:

   • Uses a suspended or robotic arm mechanism, which can offer greater flexibility in terms of print angles and directions.

   • Less common but can be seen in some experimental setups or large-scale fabrication scenarios.

8. Pellet Extruder FDM Printers:

   • Instead of filament, these use raw plastic pellets.

   • Can be more economical for large-scale prints.

   • Example: The Gigabot X.

All these printers have their own strengths and weaknesses depending on the application. For example, while Cartesian and Delta printers are popular for hobbyists and small businesses due to their ease of use and versatility, specialized types like Belt or Pellet Extruder printers might be more suited for specific tasks like continuous batch production or large-scale manufacturing.