An Alternative Parallel Mechanism for Horizontal Positioning of a Nozzle in an FDM 3D Printer

In 3D printer design, special care must be taken when choosing the print head positioning mechanism. Indeed, this choice has a significant influence on the manufacturing accuracy, printing speed, workspace characteristics, and total cost of the printer. Considering 3D printers with layer-based processes, many designs include two stages: a planar mechanism for positioning the nozzle on a horizontal plane and a linear mechanism for the vertical build-plate motion. From the literature, two designs are usually applied for horizontal motion, commercially known as "CoreXY" and "H-bot". Their load distribution characteristics are compared here: it is found that both have significant drawbacks. Therefore, an alternative architecture, called "CoreH-bot," is introduced to overcome such limitations; this mechanism is both fully planar, which greatly simplifies its design and assembly phases while increasing part life, and has low unbalanced torques during motion, which increases the maximum speed for the given accuracy. The CoreH-bot kinematic equations are analyzed to define the Jacobian matrix and the corresponding workspace. The static and dynamic analyses are also performed. A prototype with this architecture has been designed that shows interesting capabilities in terms of print speed, while being both simple and cost-effective to assemble.