Abstract:
A tilt and swivel positioning device for positioning a servo flap in a rotor blade. The device contains a tilt element and a bearing element. The tilt element is swivellably attached to the bearing element. The bearing arrangement has a convex roll-off surface resting against a concave roll-off surface. The radius of the concave roll-off surface exceeds the radius of the convex roll-off surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a tilt and swivel positioning device for positioning a servo flap in a rotor blade. The device contains a tilt element and a bearing element in which the tilt element swivels about the bearing element. 
     2. The Prior Art 
     Tilt and swivel positioning devices are used for spatial positioning of components relative to other components by tilting or swivelling movements about a swivel axis. Usually, the component is connected to the other components via a tilt or swivel joint. Furthermore, drive means or retention means are required to set the respective desired position of the component in relation to the other component. 
     Known tilt and swivel positioning devices include prestressed crank mechanisms having slide bearings or roller bearings. However, the crank-mechanisms are associated with relatively high friction losses. In addition, a change in friction forces in the dead center of movement occurs, (the so-called stick slip) making exact control of the movement sequence difficult. For some applications, roller bearings are too large or their capacity to withstand mechanical load is insufficient. 
     These disadvantages are significant when using tilt and swivel positioning devices for positioning a servo flap in a rotor blade of a helicopter. The servo flaps make it possible to vary the shape of a rotor blade to reduce aircraft noise and vibrations. Furthermore, the aerodynamics of the rotor blade can be improved. These servo flaps and bearings are also be subjected to considerable mechanical loads. In addition, the available design space is relatively small. 
     Tilt and swivel positioning devices for positioning a servo flap in a rotor blade of a helicopter are described in U.S. Pat. Nos. 5,639,215, 5,387,083 and 5,409,183. These tilt and swivel positioning devices contain the above-mentioned disadvantages. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an improved tilt and swivel positioning means. 
     This and other objects are accomplished by providing a tilt and swivel positioning device for positioning a servo flap in a rotor blade. The device contains a tilt element and a bearing element. The tilt element swivels about the bearing element. The bearing element comprises a convex roll-off surface held against a concave roll-off surface. The radius of the concave roll-off surface exceeds the radius of the convex roll-off surface. 
     Instead of crank bearings or roller bearings, there is the interaction of two roll-off surfaces. In this way, transmission of considerable forces and a highly rigid construction, even in a confined design space, is provided. The present invention also allows essentially play-free conversion of linear movement to tilting or rotational movement with little friction loss. The use of the present device for positioning the servo flap provides fast control of the aerodynamics for each individual blade, with tracking, vibration reduction, noise reduction and stall control. Overall, the aerodynamic performance is improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
     In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
     FIG. 1 shows a cross-sectional view of the device according to the invention; 
     FIGS. 2 a-c  show cross-sectional views of another embodiment according to the invention, showing three different settings; 
     FIGS. 3 a-c  show cross-sectional views of a third embodiment according to the invention, also showing three different settings; 
     FIG. 4 shows a perspective view of the tilt element of the embodiments in FIGS. 1-3 c ; and 
     FIG. 5 shows a perspective view of the end of a pull element with a push element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings and, in particular, FIG. 1 shows a partial cross-sectional view of a rotor blade having a tilt and swivel positioning device for positioning a tilt element  10  in relation to a bearing element  40 . 
     The cross-section of tilt element  10  is substantially heart-shaped on one end and comprises an outwardly concave section between two outwardly convex sections. However, as shown only in FIG. 4, tilt element  10  tapers off to a point. For ease of description, this heart shape is shown in all figures to be uniformly pointing to one side, with the outwardly convex regions and the outwardly concave region being situated on the left while the point is situated on the right. Consequently, the outwardly convex regions (left) are situated one on top of the other, so that the top and bottom directions are defined accordingly. With all interactive convex and concave roll-off surfaces, kinematic reversal is possible as well, i.e. on the respective component with a described convex roll-off surface. However, the corresponding concave roll-off surface may be provided and vice-versa. 
     The longitudinal extension of tilt element  10  is cylindrical, i.e. the longitudinal cross-section remains essentially the same. In addition, tilt element  10  is hollow and has a varying cross-sectional wall thickness. In particular, the convex and concave regions are designed to be stronger than the remaining areas because they are subject to greater loads. 
     The outer surface in the outwardly concave area forms an outer concave roll-off surface  50  for a middle convex roll-off surface  60  of bearing element  40 . The radius of outer concave roll-off surface  50  exceeds that of middle convex roll-off surface  60 . Roll-off surfaces  50 ,  60  are respectively formed surface sections. A special coating or hardening on the surface of these regions may also be provided. By increasing the hardness, wearing is reduced. By providing a low-friction design, by use of chromium-plating, friction losses in the event sliding movement occurs, can be reduced. 
     Tilt element  10  and bearing element  40  are arranged such that middle convex roll-off surface  60  of bearing element  40 , and outer concave roll-off surface  50  of tilt element  10  maintain contact with each other. Bearing element  40 , in the region of middle convex roll-off surface  60 , along the same first axis a 1  as tilt element  10 , is cylindrically shaped, so that contact occurs along the full length of elements  10 ,  40  parallel to axis a 1 . In this way, tilt and swivel movements are essentially free of any play. 
     Because tilt element  10  is hollow, an outer surface region B and an inner surface region A is provided. Outer concave roll-off surface  50  is formed in the outer surface region B. 
     Above and below the interior of outer concave roll-off surface  50 , the following are provided: the outward bulging sections of the heart shaped tilt element  10  (and thus in the interior surface region A of tilt element  10 ), and an upper and a lower inner concave roll-off surface  51  and  52 . Upper inner concave roll-off surface  51  is in contact with an upper convex roll-off surface  61  of an upper push element  21 . Lower inner concave roll-off surface  52  is in corresponding contact with a lower convex roll-off surface  62  of a lower push element  31 . The radius of concave roll-off surfaces  51  and  52  exceeds that of convex roll-off surfaces  61  and  62 . 
     Push elements  21  and  31  are arranged in the interior of hollow tilt element  10 , and are designed to be cylindrical along a second axis a 2  or a third axis a 3 . These axes are parallel to first axis a 1  of tilt element  10  so that contact takes place along the entire length. 
     Each of push elements  21  and  31  is connected to an upper and lower pull element  20  and  30 . Upper and lower pull elements  20  and  30  penetrate the mantle of tilt element  10  at an upper and lower opening  25  and  35 . As shown in more detail in FIG. 4, openings  25  and  35  are slots which extend from top to bottom in their longitudinal direction are larger than the circumference of pull elements  20 ,  30 . Consequently, it is possible to move tilt element  10  without tilting pull elements  20  and  30  horizontally or without sliding them along the vertical. 
     FIGS. 2 a - 2   c  shows the operation of an embodiment of the invention showing several settings of the tilt and swivel positioning device. In each instance, outer ends  29  and  39  of pull elements  20  and  30  are connected with piezoelectric actuators  100  and  110 . 
     Piezoelectric actuators  100 ,  110  are ceramic elements, which change their length essentially proportional to an electrical voltage present at the elements. As a rule, such actuators comprise a multiple number of interconnected piezoceramic layers. The length changes in the direction of the layer so that the changes in length of the individual layers add up. Consequently, such piezoelectric actuators are well-suited to pushing, but in the case of tension loads there is a danger that individual layers will be torn apart. In the present case, the actuators are used under a tension load. To this effect, the use of piezoelectric actuators with a transmission mechanism and a bias spring, as described in German Patent Application 197 39 594 A1, which is hereby incorporated by reference, is advantageous. 
     In FIG. 2 a , the same electrical voltage (U 1 =U 2 ) is present at both piezoelectric actuators  100  and  110 , so that their length is the same. Consequently, tilt element  10  is in a middle position, aligned horizontally. The middle position corresponds to the middle electrical voltage which is maximally applied to the actuators, so that the following applies: U 1 +U 2 =U max  and U 1 =U 2 =U max /2. 
     In FIG. 2 b , upper piezoelectric actuator  100 ′ is lengthened by an increased voltage while a lower actuator  110 ′ is correspondingly shortened by a lower voltage. If actuators  100 ′ and  110 ′ starting from the state shown in FIG. 2 a  are set accordingly, then the actuators are controlled differentially, i.e., the change in voltage on one actuator ΔU 1  has the same amount but the reversed sign as the change in voltage ΔU 2  on the other actuator: ΔU 1 =−ΔU 2  (thus the following applies: the sum of both voltages U 1 , U 2  equals the maximum voltage U max  which can be applied to an actuator: U 1 +U 2 =U max ). As a result, the lower, outwardly convex region of heart-shaped tilt element  10  is pulled to the left, while at the same time the upper, outwardly convex region of heart-shaped tilt element  10  is moved to the right. Consequently, tilt element  10  is tilted downward. As a result, two antiparallel linear movements are converted into a tilt or swivel movement. 
     In FIG. 2 c , a lower piezoelectric actuator  100 ″ is lengthened by an increased voltage while an upper actuator  110 ″ is correspondingly shortened by a lower voltage. Consequently, tilt element  10  is tilted upward. To reach the state shown in FIG. 2C, starting from the state shown in FIG. 2 a  or FIG. 2 b , the upper, outwardly convex region of the heart-shaped tilt element  10  is pulled to the left, while at the same time the lower, outwardly convex region of the heart-shaped tilt element  10  is moved to the right. Consequently, two antiparallel, linear movements are converted into a tilt or swivel movement. 
     FIGS. 3 a - 3   c  show the operation of another embodiment. Only outer end  29  of upper pull element  20  is connected to piezoelectric actuator  100 . By contrast, outer end  39  of lower pull element  30  is connected to a tension spring  120  which is attached to a wall or a frame  130 . 
     In FIG. 3 a , a medium voltage is present at piezoelectric actuator  100 , so that tension spring  120  and actuator  100  are equal in length. Consequently, tilt element  10  is in a middle position, aligned horizontally. Since only the resulting total length of pull element  20  and  30  and actuator  100  or tension spring  120  matters, it is possible that tension spring  120  in this position is different in length from the actuator, and that pull elements  20  and  30  differ accordingly in length. 
     In FIG. 3 b , upper piezoelectric actuator  100 ′ is lengthened as a result of increased voltage, while tension spring  120  is correspondingly contracted. As a result, tilt element  10  is tilted downward. To get from the state shown in FIG. 3 a  to the state shown in FIG. 3 b , the lower outwardly convex region of the hearth-shaped tilt element  10  is pulled to the left, while at the same time the upper, outwardly convex region of the heart-shaped tilt element  10  is moved to the right. As a result, two antiparallel linear movements are converted to a tilt or swivel movement. 
     In FIG. 3 c , upper piezoelectric actuator  100 ″ is shortened by a reduced voltage while tension spring  120  is extended accordingly. Consequently, tilt element  10  is tilted upward. To get from the state shown in FIG. 3 a  or FIG. 3 b  to the state shown in FIG. 3 c , the upper outwardly convex region of the heart-shaped tilt element  10  is pulled to the left, while at the same time the lower outwardly convex region of the heart-shaped tilt element  10  is moved to the right. As a result, two antiparallel linear movements are converted to a tilt or swivel movement. 
     FIG. 4 shows a perspective view of tilt element  10  of one of the embodiments in FIGS. 1-3 c . This view shows the design of upper and lower openings  25  and  35  through which upper and lower pull elements  20  and  30  penetrate the mantle of tilt element  10 . Openings  25  and  35  are slots that extend from top to bottom and in the longitudinal direction are larger than the circumference of pull elements  20 ,  30 . Consequently, it is possible to move tilt element  10  without tilting pull elements  20  and  30  horizontally or without sliding them along the vertical. 
     FIG. 5 shows a perspective view of the end of pull element  20  with push element  21 . In the region which is connected to pull element  20 , push element  21  is reinforced due to the greater forces experienced. 
     An alternative to the embodiment shown in FIG. 1 is to design outer roll-off surface  50  of tilt element  10  so that it is convex and design middle roll-off surface  60  of bearing element  40  so that it is concave. The same applies to the remaining pairs of roll-off surface. 
     As an alternative to the piezoelectric actuators shown in FIGS. 2 a - 2   c  and  3   a - 3   c , servomotors may be used. For example, it is possible to provide a toothed rack at pull elements  20  and  30  having gearwheels coupled to the servomotors for engaging the toothed racks, or it is possible to use traction cables. 
     Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.