Passive Joint Braking: A Solution to Unstable Singularity

Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. This paper considers the application of additional kinematic constraint through passive joint braking in the close neighborhood of unstable poses. The braking technique provides kinematic stability without requiring a priori knowledge of the location of unstable poses, changes in mechanism architecture, or undesirable actuator redundancy. The analysis of the braking technique is supported with analytical results using a planar Stewart Platform.