Patent US 5,656,903

Both a pneumatic, linear actuator operating as a slave actuator and a master linear actuator formed by an electric motor driven screw mechanism are linked to drive a load. The high accuracy master linear actuator has a conventional control system which dominates the control of load position or other control variable. A force sensor detects the force applied to the load by the master actuator or the force is calculated by a computer and the sensed force signal is applied to a slave actuator control to cause the slave to apply a supplemental force, typically considerably greater than the master actuator force, to the load as a function of the master actuator force. This obtains the high accuracy characteristic of the master actuator system simultaneously with the high force characteristic of the slave actuator.