  As a well understood classical fact, non- minimum phase zeros of the process
located in a feedback connection cannot be cancelled by the corresponding poles
of controller since such a cancellation leads to internal instability. This
impossibility of cancellation is the source of many limitations in dealing with
the feedback control of non-minimum phase processes. The aim of this paper is
to study the possibility and usefulness of partial (fractional-order)
cancellation of such zeros for undershoot-less control of non-minimum phase
processes. In this method first the non-minimum phase zero of the process is
cancelled to an arbitrary degree by the proposed pre-compensator and then a
classical controller is designed to control the series connection of these two
systems. Since plants with multiple non-minimum phase zeros and oscillatory
poles are very common in the problems related to robotics, the proposed method
is applied to these systems to confirm its effectiveness.
