Design and control of cross-coupled mechanisms driven by AC brushless   servo motors
  This paper presents an overview of a design methodology for the optimal synthesis of hybrid mechanisms. Hybrid mechanisms have been defined as multi-degree of freedom systems where the input motions are supplied by different motor types. In this work a five bar mechanism is designed for a given task under the constraint that one input axis rotates with constant velocity whilst the other input can exhibit any motion requirement. A machine of this type is classified as being cross-coupled due to the mechanical linkage between the input axes. Cross-coupling implies that the input motion on one axis effects the position of the other input axis. This can lead to either opposition to, or accentuation of the control system input. Such a system as this is difficult to control due to the compensation for this on each axis leading to further disturbance. Results are presented for a real machine operating in this way and the actual output of the machine is compared to the desired input of the machine. 
Andy M. Connor
math.OC