Singularities of a Manipulator With Offset Wrist

The singularities of manipulators with offset wrists are difficult to enumerate. This article presents a numerical study to illuminate singularity problems when using an offset wrist with an articulated regional arm. Ironically, the regional manipulator singularity problem is worsened when using a singularity-free offset wrist. No wrist singularities exist (they are forced by design to lie outside of joint limits). However, the existing regional arm singularities become skewed from the well-known singular configurations of common manipulators. The wrist offset also skews the well-known wrist singularities (though they hopefully still lie outside of joint limits, their locations are no longer easily determined). Thus, a zero-offset singularity-free wrist is preferable with regard to overall manipulator singularities.