• reconfigurable joint for robotic applications
  • reconfigurable actuation on two distinct axes
  • universal joint 
  • automatic reconfiguration


The Machine Mechanics research group designed a reconfigurable spherical joint for parallel robotics applications. In particular, such device is conceived as a spherical joint with lockable axes, design with the purpose of modifying the kinematics characteristics of minor mobility parallel kinematics machines. In other words, the joint is able to self-reconfigure its structure to modify the motion capabilities of the whole manipulator. In its latest version, the device is optimized for being applied to reconfigurable 3-URU robot, able to perform motions of pure rotation or pure translation. The key idea is that of locking one at a time the rotations allowed by a spherical joint by acting on a mechanical switch. Such local mechanical reconfiguration allows to radically modify the kinematic behaviour of the moving platform.

In its early versions, the reconfigurable spherical joint was not able to handle actuated axes, thus it could not be applied to joints to which a motor was connected. At present, the Machine Mechanics group has developed the prototype of a reconfigurable joint capable of provide actuation on two different axes (one at a time) of a kinematic chain. The current prototype has an extremely small footprint (a sphere with a diameter of 14 cm) thanks to the particular design of its movable components, made on concentric spherical shells able to rotate around a common centre avoiding the mutual interferences among the various levels of the device.

The figure represents the slider (red) which is moved by a bevel gear (blue) by a nut-screw coupling; this portion of the mechanism is devoted at operating the reconfiguration of the actuated axis within the spherical pair.

The engine (green) brings motion to the actuated axis through a series of bevel gears (green). The servo actuator (blue) is in charge of operating the reconfiguration which allows to move the carrier (orange) or the fork (light blue).


  • Palpacelli, M., Carbonari, L., Palmieri, G., & Callegari, M. (2018). Design of a Lockable Spherical Joint for a Reconfigurable 3-URU Parallel Platform. Robotics7(3), 42.
  • Palpacelli, M. C., Carbonari, L., & Palmieri, G. (2016). Details on the design of a lockable spherical joint for robotic applications. Journal of Intelligent & Robotic Systems81(2), 169-179.
  • Palpacelli, M., Carbonari, L., & Palmieri, G. (2014, September). A lockable spherical joint for robotic applications. In Mechatronic and Embedded Systems and Applications (MESA), 2014 IEEE/ASME 10th International Conference on (pp. 1-6). IEEE.