Abstract: A modular vibratory force generator (10) is adapted to be mounted on a helicopter fuselage (11) and operated to selectively apply a controllable vibratory force (F.sub.R) thereto. The improved generator includes a plurality of force-generating modules (12, 12) and a closed-loop servocontroller (13). Each module has a pair of counter-rotating eccentric masses (20, 21) that are arranged to exert a fixed-amplitude variable-phase individual force at spaced locations on the fuselage. These individual forces (F.sub.1, F.sub.2) combine to exert a controllable-amplitude resultant vibratory force (F.sub.R) on the structure. The servocontroller is adapted to be supplied with a single sinusoidal control signal and is operative to cause the frequency and phase of the resultant vibratory force to be identical to the frequency and phase of the control signal and to cause the amplitude of the resultant vibratory force to be proportional to the amplitude of the control signal.

Abstract: An actively-controlled resonant-type force generator (20) is adapted to be attached to a structure (21), and includes a mass (23) mounted for movement relative to the structure and a plurality of springs (22, 24) operatively arranged between the mass and the structure. A servoactuator (26) is arranged to controllably excite the mass-spring system. The actual force (F.sub.a) transmitted from the mass to the structure is compared with a commanded force (F.sub.c) to produce a force error signal (F.sub.e). The actuator is caused to produce a velocity as a function of the error signal. The gain of the closed force loop is selected so that the resonance of the mass-spring system has an effective damping ratio (.zeta.) greater than about 0.5, and preferably about 0.7. Thus, the mass-spring system will not be substantially resonantly excited by vibrations of the structure near its resonant frequency (.omega..sub.n).

Abstract: An improved motion simulator (10) includes a base (11), a capsule (14) having an at least partially-spherical smooth outer surface (15). The capsule is capable of roll, pitch and yaw angular motions about a pivot point (16) at the center of the spherical surface, and is also capable for upward and downward heave motion of the pivot point along a vertical axis (z--z) relative to the base. Actuators (33, 34, 35) are operatively arranged to selectively move the capsule relative to the base in any of four degrees of freedom. The capsule outer surface is configured such that no possible motion of the capsule in any of the permissible four degrees of freedom will cause any portion of the capsule to move outside of a motion envelope formed by an imaginary vertical cylinder (41 ) having a diameter (d) substantially equal to that of the spherical surface.

Abstract: A method of controlling the application of counter-vibration to a structure (20) so as to reduce the effect of externally-created sinusoidal vibration thereon includes the steps of: mounting a vibratory force generator (19) on the structure; mounting an accelerometer (21) on the structure at a point at which vibration is to be measured; providing a tunable filter (16) capable of resonating at an electrically-controllable frequency; providing an adaptive frequency estimator (22) arranged to produce a tuning signal (.theta.

Abstract: An actively-controlled resonant-type force generator (20) is adapted to be attached to a structure (21), and includes a mass (23) mounted for movement relative to the structure and a plurality of springs (22, 24) operatively arranged between the mass and the structure. A servoactuator (26) is arranged to controllably excite the mass-spring system. The actual force (F.sub.a) transmitted from the mass to the structure is compared with a commanded force (F.sub.c) to produce a force error signal (F.sub.e). The actuator is caused to produce a velocity as a function of the error signal. The gain of the closed force loop is selected so that the resonance of the mass-spring system has an effective damping ratio (.zeta.) greater than about 0.5, and preferably about 0.7. Thus, the mass-spring system will not be substantially resonantly excited by vibrations of the structure near its resonant frequency (.omega..sub.n).

Abstract: A fluid-powered actuator (42) has a body (11) which includes an end wall (16) provided with a through-opening (21). A piston rod (44) has an inner portion (44A) arranged on one side of the end wall within a pressurizable working chamber (24) of the actuator, has a penetrant portion (44B) passing through the end wall opening, and has an outer portion (44C) arranged on the other side of the end wall. The rod is configured such that the transverse cross-sectional area of the penetrant portion is greater than the transverse cross-sectional area of the outer portion so as to define an annular surface (46) which faces away from the actuator chamber. The improvement provides a seal assembly (43) for containing fluid leaking from the actuator chamber.

Abstract: A device (19) for generating a rotating force vector and an oscillatory couple includes a plurality of non-concentric eccentric masses (22A, 22B, 22C, 22D, 22E, 22F) co-rotating at the same angular speed; and means (24A, 24B, 24C, 24D, 24E, 24F) for individually controlling the angular position of each of the masses; whereby, by selectively controlling the angular position of each eccentric mass, the device may generate a desired rotating force vector and a desired oscillatory couple. In use, the device performs an improved method for opposing the propagation of vibration from a dynamically unbalanced rotating rotor through a supporting structure (12).

Abstract: An improved two-stage servovalve (70) has a pilot-stage and an output-stage. A torque motor (16) produces pivotal movement of a flapper (18) in response to a supplied electrical current. The pilot-stage produces a flow which is used to selectively displace a second-stage spool (61) relative to a body bore. The servovalve has a hydromechanical pressure feedback loop closed about the load and second-stage spool. The pressure feedback loop is intertwined with an electrical spool position feedback loop closed about the spool and driver. The command to the pressure loop is a function of the error of the spool position loop. The gain of the spool position loop dominates that of the pressure loop. The valve has pressure-flow characteristics approximating those of a "flow-control" servovalve but affords access to an electrical signal substantially proportional to the load pressure differential.

Abstract: A vibration isolator is operatively associated with a suspension having a spring (21) and a fluid damper (22) arranged in parallel with one another between two masses (23, 24) which are arranged to move relatively toward and away from one another. A restricted orifice (33) communicates the opposed damper chambers (30, 31). The vibration isolator includes a fluid pump (46) and an actuator (48) for operating the pump. The pump has a first chamber (51) communicating with the damper first chamber (30), and has a second chamber (52) communicating with the damper second chamber (31). The pump is selectively operated so as to create a pressure differential across the orifice to oppose and substantially cancel the dynamic force transmitted through the spring and damper and attributable to high-frequency relative vibration between the masses, while permitting the damper to damp low-frequency relative velocity between the masses.

Abstract: A lase diode light source (21) is arranged to emit light of a desired intensity (I1), which is transmitted via an optical conductor (22). Light exiting the fiber has an intensity (I.sub.2), and falls incident on the receiver surface of a photodiode (23). Such transmitted light provides both the power and control for operating a load (24). The load has a maximum impedance such that the maximum load input voltage required to produce the maximum desired load current does not exceed the forward conductive breakdown voltage of the photodiode.

Abstract: An "active" suspension system provides two parallel force-transmitting paths between the body and wheel of a vehicle. The first path has a main spring (41), and the second path includes an actuator (42) and a spring (43). LVDT's (53,55) are arranged to monitor the displacements of the actuator (42) and the spring (43). The actuator is arranged in a high-gain closed position or velocity servoloop. The actual force (F.sub.w) exerted by the suspension system on the body is determined and compared with a desired force (F.sub.c) to produce a force error signal (F.sub.e). The force error signal (F.sub.e) is converted to a command signal supplied to the servoloop. The servoloop operates the actuator (42) so as to continuously drive the force error signal (F.sub.e) toward zero.

Abstract: An improved energy-conserving servoactuator has at least one valve operatively associated with a double-acting fluid-powered actuator. When a load is applied to the actuator, the pressure in one actuator chamber will be greater than in the other. If the load is "opposing" with respect to the desired direction of actuator movement, fluid is supplied to the higher pressure chamber and is permitted to flow from the lower pressure chamber. However, if the load is "aiding" with respect to the desired direction of actuator movement, fluid in the higher pressure chamber is permitted to flow into the lower pressure chamber without drawing fresh fluid from the source.

Abstract: A seal assembly is arranged to contain leakage of hydraulic fluid passing between a wall opening and a penetrant rod portion passing through the opening. The seal assembly includes a sliding-seal member mounted on a portion of the rod for sliding movement toward and away from an abutment surface and a non-sliding flexible-seal member arranged between the body and the sliding-seal member. The body, flexible-seal member, sliding-seal member and rod define a sealed chamber into which such fluid will leak. The chamber communicates with a fluid reservoir through a oneway check valve. The sliding-seal and flexible-seal members are arranged in parallel with one another. In one embodiment, a spring urges the sliding-seal member to move toward an abutment surface provided on the rod. In another embodiment, movement of the sliding-seal member relative to the body is limited by facing abutment steps.

Abstract: An equalizer is arranged to continuously sense the control pressures of two valves. In the event of a differential between the control pressures, the equalizer operates to selectively adjust one valve so that the control pressures of both valves will thereafter be substantially equal.

Abstract: An improved electrohydraulic servovalve has first and second valve spools mounted for independent sliding movement relative to a body in response to a common command signal. The valve has a first drive mechanism operatively arranged to cause a desired motion of one valve spool in response to the command signal, and has a second drive mechanism operatively arranged to cause a desired simultaneous similar motion of the other valve spool in response to the command signal. The improvement comprises a differential position sensing mechanism arranged to sense the relative positions of the two valve spools and operative to produce an output related to the difference therebetween, and an indicating device supplied with such output and operative to indicate substantially dissimilar relative positions of the spools.