Modeling and design of flexure jointed Stewart platforms for control purposes

A number of researchers have been investigating the use of Stewart platforms (or hexapods) for precision applications including machining, vibration isolation and precise pointing. To avoid friction and backlash, these hexapods often employ flexure joints. This does eliminate nonlinear friction and backlash, but adds linear spring/damper dynamics. In addition, since the motion is so accurate, base and/or payload vibrations become significant disturbances to suppress. This paper develops guidelines for designing the flexure joints to facilitate closed-loop control. In addition, since base accelerations are typically the dominant disturbance, their effect is derived. Unlike most prior hexapod dynamic formulations, the model is experimentally verified.