Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-09-16
2004-04-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06717333
ABSTRACT:
BACKGROUND
The present invention relates to a piezoelectric actuating device for controlling the flaps on the rotor blade of a helicopter, including a piezo element arrangement that contains at least one piezoelectric stack actuator, and further including a power transmission frame which is coupled to the piezo element arrangement and attachable to a rotor blade and which generates a force between an abutment and a driven element, which are provided on the power transmission frame, from a change in length of the piezo element arrangement upon excitation thereof, the force acting transversely to the direction of the centrifugal force of the rotor blade, provision being made for a first holding device via which the power transmission frame can be fixed to the rotor blade in the direction of the centrifugal force but which is flexible transversely to the direction of the centrifugal force and which allows the power transmission frame to move transversely to the direction of the centrifugal force relative to the rotor blade within a limited range; and provision being made for a second holding device which fixes the abutment, which is provided on the power transmission frame, transversely to the direction of the centrifugal force relative to the rotor blade but is flexible in the direction of the centrifugal force and which allows the abutment to move in the direction of the centrifugal force relative to the rotor blade within a limited range.
Piezoelectric actuating devices are increasingly used in many fields of application and can be used to advantage especially in aerospace due to their small size and their high power density. Because of their high power density, piezoelectric actuating devices are particularly suitable for controlling the flaps on the rotor blades of helicopters. In this context, however, it is a problem that the piezoelectric actuating device must be guaranteed to be securely supported and decoupled against the centrifugal force (of up to 1000 g) occurring at the rotor blade.
German Patent DE 196 46 676 C1 and German Patent Application DE 196 48 545 A1 describe piezoelectric stack actuators in the form of stacked individual piezoelectric elements as could be provided in a piezo element arrangement contained in a piezoelectric actuating device and used for driving the same.
Moreover, U.S. Pat. Nos. 4,808,874 and 4,952,835 describe piezoelectrically driven amplifier mechanisms which amplify a stroke movement without using levers or motors.
Furthermore, U.S. Pat. No. 5,907,211 describes piezoelectric actuator which has an X-shaped configuration and is operated by two piezoelectric elements. The actuator is arranged within a housing, the actuation being accomplished via a corresponding displacement plate. Moreover, the actuator is attached to the housing by flexible holding devices which are formed in one piece. The actuator is used, for example, for controlling the servoflap of a rotor blade of a helicopter.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a piezoelectric actuating device for controlling the flaps on the rotor blade of a helicopter which features a high degree of performance reliability and operational safety and at the same time markedly reduces the risk of damage to the piezoelectric element.
The present invention provides a piezoelectric actuating device for controlling the flaps on the rotor blade of a helicopter, including a piezo element arrangement that contains at least one piezoelectric stack actuator, and further including a power transmission frame which is coupled to the piezo element arrangement and attachable to the rotor blade and which generates a force between an abutment and a driven element, which are provided on the power transmission frame, from a change in length of the piezo element arrangement upon excitation thereof, the force acting transversely to the direction of the centrifugal force of the rotor blade, provision being made for a first holding device which fixes the power transmission frame on the rotor blade in the direction of the centrifugal force but is flexible transversely to the direction of the centrifugal force and which allows the power transmission frame to move transversely to the direction of the centrifugal force relative to the rotor blade within a limited range and provision being made for a second holding device which fixes the abutment, which is provided on the power transmission frame, transversely to the direction of the centrifugal force relative to the rotor blade but is flexible in the direction of the centrifugal force and which allows the abutment to move in the direction of the centrifugal force relative to the rotor blade within a limited range. According to the present invention, the first holding device contains two arrangements of first flexurally soft straps extending essentially parallel to each other in the direction of the centrifugal force, and the second holding device contains two arrangements of second flexurally soft straps extending essentially parallel to each other transversely to the direction of the centrifugal force which will allow the flexurally soft straps of the first holding device and of the second holding device to perform a parallelogram movement.
The piezoelectric actuating device has an advantage of being reliably and securely fixed against the high centrifugal force occurring at the rotor blade of a helicopter without thereby impairing the performance reliability of the actuating device.
Advantageously, the first holding device includes first holding elements which extend longitudinally in the direction of the centrifugal force and which are attached to the rotor blade at one end and to the power transmission frame of the actuating device at the other end. These guarantee that the power transmission frame is reliably supported against the centrifugal force, the driven element and the abutment at the same time being allowed to move without restriction in the manner intended for this.
Preferably, the first holding elements are formed of straps which are flexurally soft transversely to the direction of the centrifugal force of the rotor blade. Such straps allow the power transmission frame to move without restriction transversely to the direction of the centrifugal force, the power transmission frame at the same time being reliably fixed in the direction of the centrifugal force. Moreover, the use of such flexurally soft straps allows the power transmission frame to be fixed in the third direction as well, i.e., in a direction perpendicular to the plane defined by the direction of the centrifugal force and the intended direction of motion of the abutment and the driven element.
Preferably, the first holding device contains two arrangements of first flexurally soft straps extending essentially parallel to each other in the direction of the centrifugal force. This permits a quasi parallelogram movement of the flexurally soft straps relative to the power transmission frame and relative to a centrifugal force fastener which is provided on the rotor blade and to which the first holding elements are fixed. In an embodiment, each of the two arrangements of first flexurally soft straps contains only one such strap so that the power transmission frame is held by two first straps running parallel to each other in the direction of the centrifugal force.
On the side of the power transmission frame, the first holding elements are advantageously attached to the abutment or in the vicinity thereof or to the driven element or in the vicinity thereof, respectively.
According to an embodiment of the piezoelectric actuating device according to the present invention, the second holding device includes second holding elements which extend transversely to the direction of the centrifugal force and are connected to the abutment at one end and, at the other end, to a fastening element which is used for attachment to the rotor blade. This allows the power transmission frame of the actuating device to move in a defined manner in the direction of the centrifugal for
Hermle Frank
Jaenker Peter
Davidson Davidson & Kappel LLC
Dougherty Thomas M.
EADS Deutschland GmbH
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