Synchronized travel of independent actuators

A combination comprising:

• a pair of bidirectional hydraulically powered linear actuators each having a piston reciprocable between extended and retracted positions;
• a source of pressurized fluid for operating the actuators;
• means monitoring the motion of each actuator and providing an indication of a dissimilarity between operating motions of the actuators, the means for monitoring including a differential gear motion sensing device and a pair of mechanical feedback members each having one end fixed to a corresponding piston for reciprocation therewith and the other end drivingly coupled to the differential gear motion sensing device;
• and
• means including means for determining the direction of travel of each actuator and responsive to a dissimilarity indication for retarding the flow of operating fluid from the source to an appropriate one of the actuators to diminish the dissimilarity between the operating motions of the actuators, the appropriate one actuator being the actuator with the greater extension when the actuators are transitioning from the retracted toward the extended position and the actuator with the lesser extension when the actuators are transitioning from the extended toward the retracted condition.

A combination comprising:

• a pair of bidirectional fluid powered actuators;
• a source of pressurized fluid for operating the actuators;
• means monitoring the motion of each actuator and providing an indication of a dissimilarity between operating motions of the actuators;
• and
• means including a pair of throttling valves responsive to a dissimilarity indication for retarding the flow of operating fluid from the source to an appropriate one of the actuators to diminish the dissimilarity between the operating motions of the actuators, the throttling valves retarding the flow of actuating fluid from the source to said one actuator while leaving unchanged the flow of actuating fluid from the source to the other actuator in response to a dissimilarity indication to diminish the dissimilarity between the motions of the two actuators.

A method of coordinating the responses of two fluid powered actuating devices as they respond to fluid flows to move respective objects between initial and final positions to assure that both objects begin moving from their corresponding initial positions at the same time and simultaneously arrive at their corresponding final positions comprising the steps of:

• simultaneously initiating the flow of fluid to the two actuating devices;
• continuously monitoring the progress of the objects toward their final positions;
• error sensing for a lack of synchronization between the two objects, and for an indication of which object is moving too rapidly so as to arrive at its final position before the other object arrives at its final position;
• and
• adjusting the flow of fluid to at least one of the actuating devices in response to the error sensing to cause the objects to arrive at their respective final positions more nearly simultaneously.