A new rotary hexapod for micropositioning

Abstract

Hexapods are widely used for precision positioning, but their workspace is too limited for some applications. Often, a rotary stage is added to enlarge the orientation workspace, but this increases the system cost. As an alternative, rotary hexapods have been proposed in which the legs are of fixed length and the base attachment points slide along a common circular path. However, these hexapods have a reduced range of motion in some degrees of freedom due to mechanical interferences. In contrast, we propose a design in which two concentric circular rails are used in addition to double spherical joints, three extra rotary sensors, and two high-accuracy rotary encoders. As a result, the workspace of our robot is significantly increased, its direct kinematics can be solved linearly, and its high accuracy is guaranteed. A prototype has been built and is described in detail.