D-H parameters augmented with dummy frames for serial manipulators containing spatial links

Conventional kinematic studies of serial manipulators involve the proper selection of coordinate frames of reference at appropriate positions. The standard practice, being used in the past, is the use of Denavit-Hartenberg (D-H) algorithm for assigning coordinate frames. However, it has been observed that when an open kinematic chain contains a spatial link with two consecutive joint axes at right angle to each other, the forward kinematics derived with D-H algorithm comes geometrically inconsistent. A typical spatial link involves more than one non-zero link/joint parameters, which are not being accounted for, in the corresponding D-H parameter table. Forward kinematic study of manipulators involving spatial links with two consecutive joint axes at right angles to each other leads to recognizable deficiency of the D-H algorithm, as one of its practical limitation. In the present work, the concept of dummy frames is proposed to eliminate this deficiency. The proposed concept is demonstrated successfully for the case study of a Manipulator for Medical Application (MMA), which is a seven degrees-of-freedom (DOF) manipulator containing spatial links. Both geometrical and physical validation is performed to ensure the efficacy of the proposed concept.