Load equilization feedback for parallel channel servo actuators

#In applications requiring force transmission in hydraulic systems, there is a desirability for utilization of actuator pairs. In the prior art when the actuators are arranged in parallel, a very small differential in pressure across the pistons in each of the actuators can result in a mismatch in piston movement within the cylinders. Such mismatch in piston movement (differential movement between the pistons) results in a lateral deflection of the actuators. Such lateral deflection impairs performance of the actuator pair and thus reduces the reliability thereof. In addition, the pistons, as a result of the lateral deflection, may bind within the cylinders, thereby reducing the life of the actuators through unusual wear of the pistons, the seals and the internal cylinder walls.

#To correct the foregoing problems, when the application requires the utilization of parallel actuators, very complicated pressure synchronization systems must be employed. Such complicated systems in turn reduce the reliability and increase the cost of manufacture as well as maintenance of the system.

#Mechanical feedback apparatus having a load synchronization capability in a parallel actuator pair force transmission system which includes separate control valves for each of the actuators, means connected to the actuators to detect differential motion therebetween and means for applying the detected differential motion to the control valve means in a phase such as to counteract the differential motion.

#FIG. 1 is a perspective view of a parallel actuator pair including the mechanical feedback apparatus having load synchronization capability in accordance with the present invention;

#FIG. 2 is an exploded view of a partially disassembled actuator pair as illustrated in FIG. 1 more clearly illustrating the mechanical feedback apparatus having the load synchronization capability;

#FIG. 3 is a schematic diagram, partly in cross section illustrating differential motion between a parallel actuator pair and the results thereof;

#As shown in FIG. 1, a parallel actuator pair 8 includes a pair of cylinders 10-12 housing a pair of reciprocally movable pistons (not shown) to which are connected piston rods 14-16, respectively. Appropriate fittings 18-20 are associated with the cylinders and piston rods, respectively, to mount the actuator pair in accordance with any desired application for the transmission of force. One example of use is as to a control surface in an aircraft as reciprocal relative movement between the piston rods and the cylinders occur through application of fluid under pressure across the pistons. A mechanical feedback linkage 22 overlies said cylinders 10-12 and is connected through a summing link 24 and an input link 26 through an adjustable link 28 to the control valve input 30 of the control valve 32. The input link 26 may also include a connection 34 for receiving input signals from flight control mechanisms such as the pilot, auto-pilot, or flight augmentation systems, as is well known. The system as thus described, including the actuator pair with an appropriate feedback, summing and input linkage is well known and operates in accordance with well understood principles. However, such a structure as generally described will not automatically counteract for mismatch between the actuator pair.

#As more clearly shown in FIG. 2, to which reference is hereby made, through the utilization of a summing link 24 which is flexible in torsion, any differential motion between the piston rods 14-16 will be applied to the control valves 32. As is shown in FIG. 2, the summing link 24 includes a first leg 36 and a second leg 38 interconnected by a flexible web 40. The legs 36 and 38 of the summing link 24 are anchored at the ends 42 and 44 thereof to lugs 46 and 48 provided on the cylinders 10-12 respectively. The opposite ends 50-52 thereof are connected to spaced apart arms 54 and 56, respectively of the feedback linkage 22. The opposite end 58 of the feedback linkage is connected to the fitting 20 (FIG. 1) on the piston rods 14-16. The fitting 20 couples the piston rod ends together to cause them to move as a unit.

#The input linkage 26 is in turn connected at points 60 and 62 on the summing linkage 24, which points are intermediate the ends of the arms 36 and 38, respectively. As is illustrated, the input linkage 26 includes first and second legs 61 and 63. The leg 61 is connected at one end 64 thereof to the end 66 of the adjustable link 28. The end 68 of the leg 63 is connected to the end 70 of the adjustable link 28'. The opposite ends 72 and 74 of the adjustable links 28--28', respectively, are in turn connected to the input 30 of the control valves 32 for the actuator 10 and the control valve 33 for the actuator 12. As shown the cylinders 10-12 overlie the control valves 32-33 respectively, and are formed as part of the same housing.