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.

Cable-suspended robots may move beyond their static workspace by keeping all cables under tension, thanks to end-effector inertia forces. This may be used to extend the robot capabilities, by choosing suitable dynamical trajectories. In this paper, we consider three-dimensional (3D) elliptical trajectories of a point-mass end effector suspended by three cables from a base of generic geometry. Elliptical trajectories are the most general type of spatial sinusoidal motions. We find a range of admissible frequencies for which said trajectories are feasible; we also show that there is a special frequency, which allows the robot to have arbitrarily large oscillations. The feasibility of these trajectories is verified via algebraic conditions that can be quickly verified, thus being compatible with real-time applications. By generalizing previous studies, we also study the possibility to change the frequency of oscillation: this allows the velocity at which a given ellipse is tracked to be varied, thus providing more latitude in the trajectory definition. We finally study transition trajectories to move the robot from an initial state of rest (within the static workspace) to the elliptical trajectory (and vice versa) or to connect two identical ellipses having different centers.

Parallel robots with configurable platforms are a class of robots in which the end-effector has an inner mobility, so that its overall shape can be reconfigured: in most cases, the end-effector is thus a closed-loop kinematic chain composed of rigid links. These robots have a greater flexibility in their motion and control with respect to rigid-platform parallel architectures, but their kinematics is more challenging to analyze. In our work, we consider n-RRR planar configurable robots, in which the end-effector is a chain composed of n links and revolute joints, and is controlled by n rotary actuators located on the base of the mechanism. In particular, we study the geometrical design of such robots and their direct and inverse kinematics for $n=4$, $n=5$ and $n=6$; we employ the bilateration method, which can simplify the kinematic analysis and allows us to generalize the approach and the results obtained for the 3-RRR mechanism to n-RRR robots (with $n>3$). Then, we study the singularity configurations of these robot architectures. Finally, we present the results from experimental tests that have been performed on a 5–RRR robot prototype.