Improved dynamics and stiffness.Traditional multi-axis systems are designed in a way that the top level stage has to be supported by all the stages below it and so on, meaning that the bottom positioner has to carry all the load, significantly reducing its dynamics. All axes carry different loads, with different dynamics making tuning harder since each component has a different natural frequency. With only one common light-weighted platform carried and actuated by six parallel actuators, hexapods provide a very high stiffness and natural frequency. The lower inertia (moved mass) leads to higher dynamics, better responsiveness, and faster settling for all axes.
Freely selectable center of rotation (Pivot Point). In a serial kinematic system, motion is confined by bearings – and the center of rotation is related to the fixed radius of each rotary stage and goniometric cradle used. In order to move the center of rotation, mechanical changes, have to be made or fixturing needs to be modified. With a PI hexapod, a single software command can set the center of rotation to any location inside or outside the hexapod envelope. In PI’s multi-axis hexapod systems, the center of rotation can be changed by a single software command on the fly.
No cable management issues. With traditional multi-axis positioners, as a stage moves, cables need to be dragged along. Friction and torque generated by bending forces contribute to parasitic motions reducing accuracy and repeatability. Parallel kinematic positioners, such as hexapods, avoid moving cables altogether.
No parasitic errors. Stacked axes interact in complicated ways. For example, runout in the x-axis can cause unwanted motion in the y– and z-axes; angular deviation of an axis similarly imparts motion in the travel-directions of the other axes, with magnitude proportional to the distance to the moving axis. And in stacks, that multiplicative lever arm can be large.
