Abstract:
A vibration generator has at least two groups of shafts, on which at least two groups of imbalances are disposed, and which are connected with at least one drive that rotates the shafts relative to one another, at different speeds of rotation, thereby achieving a directed advance. The operating direction of the vibration generator can be adjusted.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicants claim priority under 35 U.S.C. §119 of European Application No. 08103166.8 filed Mar. 28, 2008. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a vibration generator comprising at least two groups of shafts, on which at least two groups of imbalances are disposed, and which are connected with at least one drive, in such a way that they are driven at different speeds of rotation. Means are provided for changing the phase position of at least two imbalance groups, relative to one another, thereby achieving targeted advance. 
         [0004]    2. The Prior Art 
         [0005]    In construction, vibration generators are used to introduce objects, such as profiles, into the ground, or to draw them from the ground, or also to compact ground material. The ground is excited by means of vibration, and thereby achieves a “pseudo-fluid” state. The goods to be driven in can then be pressed into the construction ground by a static top load. The vibration is characterized by a linear movement and is generated by rotating imbalances that run in opposite directions, in pairs. 
         [0006]    The vibration generators are vibration exciters having a linear effect, whose centrifugal force is generated by rotating imbalances. The size of the imbalance is also referred to as a static moment. The progression of the speed of the linear vibration exciter corresponds to a periodically recurring function, particularly a sine function. On the basis of the sine-shaped progression of the force effect generated by the rotating imbalance masses, a drive that acts alternately in the forward drive direction and counter to it, with time offset, is produced. In this connection, it is possible to bring about a directed force effect in the forward drive direction, by coupling with imbalances that rotate at different speeds of rotation. 
         [0007]    Depending on the stated task, however, different orientations of the operating force generated are desirable. For example, a pile-driving process requires a directed force in the forward drive direction, while a retraction process requires a force in the opposite direction. It is a disadvantage of the previously known systems that a vibration generator for introducing material to be pile-driven, having a force effect directed in the forward drive direction, cannot be used for retraction processes, or can only be used by superimposition of significant static forces. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the invention to provide a vibration generator that allows a directed effect of the force, depending on the set task, both in the pile-driving direction and in the retraction direction. According to the invention, this task is accomplished by a vibration generator comprising at least two groups of shafts, on which at least two groups of imbalances are disposed, and which are connected with at least one drive. The shafts rotate at different speeds of rotation relative to one another, thereby achieving a directed advance. There are also means for adjusting the effective direction of the vibration generator. 
         [0009]    With the invention, a vibration generator is created that allows a directed force in the forward drive direction or the retraction direction, depending on the task. In this way, adaptation of the vibration generator to different process requirements, such as pile-driving and retraction, is made possible. 
         [0010]    In an embodiment of the invention, the means for adjustment of the effect direction comprise a swivel motor by way of which the relative phase position of at least two imbalance groups that rotate at different speeds of rotation can be changed. In this way, a change in the effect direction is made possible, without any conversion measures being required. 
         [0011]    In a further embodiment of the invention, the at least two imbalance groups are connected with the swivel motor by way of gear wheels. At least one imbalance group is connected with the stator, and at least one imbalance group is connected with the rotor of the swivel motor. In this way, direct adjustment of the imbalance groups by way of the swivel motor is made possible. 
         [0012]    It is advantageous if the swivel motor is a rotary vane swivel motor. Alternatively, the swivel motor can also be a swivel motor having a steep thread. 
         [0013]    In a further development of the invention, two shaft groups are connected with the at least one drive in such a manner that the speed of rotation of the first shaft group amounts to half the speed of rotation of the second shaft group. The ratio of the static moments of the shaft groups provided with the imbalance groups amounts to between six to one and ten to one. By coupling at least two shaft groups having a speed of rotation ratio of 2:1 and a ratio of the static moment of between 6:1 and 10:1, a directed characteristic line in the forward drive direction is produced by superimposition of the sine-shaped force characteristic lines generated by the rotating imbalances. A significantly greater maximal force in the forward drive direction comes about, as compared to the opposite direction. Since the ground cannot follow the great acceleration in the pile-driving direction during the pile-driving process, the goods to be driven in uncouple from the ground, which is also vibrating, at every forward drive pulse. Because of this periodic uncoupling of ground and goods to be driven in, little energy is transferred to the construction ground. As a result, the vibration stress on the surroundings is also clearly further reduced. 
         [0014]    Preferably, the static moment of the first shaft group is eight times as great as the static moment of the second shaft group. In this way, a marked force peak in the forward drive direction is brought about. 
         [0015]    In another embodiment of the invention, three shaft groups are disposed, on which at least three imbalance groups are disposed. The shaft groups are connected with the at least one drive in such a manner that the speed of rotation of the first shaft group amounts to half the speed of rotation of the second shaft group and to one-third of the speed of rotation of the third shaft group. The ratio of the static moments of the shaft groups provided with the imbalance groups, relative to one another, amounts to essentially 100:16.64:3.68. In this way, the maximally active force is increased by a further marked force peak in the forward drive direction. As a result, a further increase in energy efficiency, connected with acceleration of the pile-driving process, is achieved. 
         [0016]    In another embodiment of the invention, there are four shaft groups on which at least four imbalance groups are disposed. The shaft groups are connected with the at least one drive in such a manner that the ratio of the speeds of rotation of the shaft groups amounts to essentially 1:2:3:4, and the ratio of the static moments of the shaft groups provided with the imbalance groups, relative to one another, amounts to essentially 100:18.72:5.6:1.38. As a result, a further particular emphasis of the force progression in the forward drive direction is achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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. 
           [0018]    In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
           [0019]      FIG. 1  is a schematic representation of a gear mechanism of a vibration generator for directed vibration, having two shaft groups; 
           [0020]      FIG. 2  shows the vibration gear mechanism from  FIG. 1 , with an additional swivel motor for changing direction; 
           [0021]      FIG. 3  is a schematic representation of a gear mechanism that acts in a directed manner, having two shaft groups, each consisting of three shafts; 
           [0022]      FIG. 4  is a schematic representation of different variants of vibrator gear mechanisms that act in a directed manner, having
       a) a six-shaft, short construction;   b) a seven-shaft, simple construction;   c) a seven-shaft, short construction;         
           [0026]      FIG. 5  is a schematic representation of vibrator gear mechanisms that act in directed manner and can change direction, having
       a) a six-shaft, simple construction; and   b) a six-shaft, short construction;         
           [0029]      FIG. 6  is a representation of the vibrator gear mechanism from  FIG. 5 , in a compact embodiment, and 
           [0030]      FIG. 7  is a schematic representation of a vibrator gear mechanism that can change direction, having eight shafts. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    Referring now in detail to the drawings, the vibration generators selected as exemplary embodiments are configured as vibrator gear mechanisms. Such vibrators consist essentially of a housing, in which shafts provided with gear wheels are mounted. The gear wheels are provided with imbalance masses, in each instance. Such vibrator gear mechanisms having imbalance masses mounted to rotate are known to a person skilled in the art, for example from German Patent No. DE 20 2007 005 283 U1. The following explanation of the exemplary embodiments is essentially limited to the arrangement of shafts and imbalance masses. 
         [0032]    In the assembly according to  FIG. 1 , two shaft groups  1 ,  2  are disposed. Shafts  11 ,  12  of shaft group  1  are provided with gear wheels  112 ,  122 , on which imbalance masses  111 ,  121 , are disposed. Imbalance masses  111 ,  121  are configured in the same manner here. Shafts  21 ,  22  of shaft group  2  are also provided with gear wheels  212 ,  222 , on which imbalance masses  211 ,  221  of the same type are disposed. Gear wheels  112 ,  122 ,  212 ,  222  are configured in such a manner that during rotation, the speed of rotation of shafts  21 ,  22  of shaft group  2  is twice as great as the speed of rotation of shafts  11 ,  12 . Imbalance masses  111 ,  121 ,  211 ,  221  are disposed in such a manner that the static moment of shaft group  1  is eight times as great as the static moment of shaft group  2 . 
         [0033]    In the embodiment according to  FIG. 2 , a swivel motor  5  is additionally disposed, whose stator has a gear wheel  51  and whose rotor has a gear wheel  52 . Shaft groups  1 ,  2  are connected with one another, by way of swivel motor  5 , in such a manner that gear wheel  112  of shaft  11  engages gear wheel  52  of swivel motor  5 ; gear wheels  212 ,  222  of shaft group  2  engage gear wheel  51  of swivel motor  5 . It is now possible to adjust a phase shift of the vibrations of shaft group  2  relative to the vibrations of shaft group  1  by relative swiveling of the rotor with regard to the stator, thereby making it possible to set a change in direction. In the present example, swivel motor  5  is a rotary vane motor having one vane. 
         [0034]    In the assembly according to  FIG. 3 , shaft groups  1 ,  2  are formed from three shafts  11 ,  12 ,  13 ,  21 ,  22 ,  23 , which are provided with imbalance masses  111 ,  121 ,  131 ,  211 ,  221 ,  231 , respectively. Gear wheels  112 ,  122 ,  132 ,  212 ,  222 ,  232  of shafts  11 ,  12 ,  13 ,  21 ,  22 ,  23 , in turn, are selected so that during rotation, the shafts of shaft group  2  demonstrate twice the speed of rotation compared to the shafts of shaft group  1 . A more compact construction can be achieved by offsetting shafts  21 ,  22 ,  23  of shaft group  2  (cf.  FIG. 4   a )). The number of shafts of the shaft groups  1 ,  2  can also be selected to be different. In the exemplary embodiment according to  FIG. 4   b ), an additional shaft  24  with a corresponding imbalance mass  241  has been added. Again, a compact construction can be achieved by means of an offset arrangement of shafts  21 ,  22 ,  23 ,  24  of shaft group  2  (cf.  FIG. 4   c )). 
         [0035]    In the embodiment according to  FIG. 5 , a swivel motor  5  is disposed between shafts  11 ,  12 ,  13  of shaft group  1  and shafts  21 ,  22 ,  23  of the shaft group  2 . In this connection, gear wheels  112 ,  122 ,  132  of shaft group  1  engage gear wheel  51  of the stator of swivel motor  5 , and gear wheels  212 ,  222 ,  232  of shaft group  2  engage gear wheel  52  of the rotor of swivel motor  5 . Again, switching of the effect direction is made possible by a relative rotation of stator and rotor of swivel motor  5 . Again, a more compact construction height can be achieved by an offset arrangement of the shafts of shaft group  2  (cf.  FIG. 5   b )). 
         [0036]    In  FIG. 6 , a modified construction of the aforementioned assembly according to  FIG. 5  is shown, which permits a clear reduction in the construction length, but in which eight shafts are required in place of six shafts. This results in less stress on the shaft bearings and brings with it advantages with regard to the centripetal force that can be achieved, suitability for high speeds of rotation, and less sensitivity with regard to great angle accelerations. 
         [0037]    To achieve the most balanced characteristic line shape possible, an additional speed of rotation stage, whose imbalances rotate at three times the speed of rotation, can be used. In the embodiment according to  FIG. 7 , such an assembly, based on the gear mechanism concept according to  FIG. 5 , is shown. This turns out to be slightly wider, since the lower large gear wheel  132 , which drives the two shafts  31 ,  32 , which are disposed next to one another, is displaced relative to the center of the gear mechanism. In the adjustment of the effect direction, the angle setting of slow imbalances  111 ,  121 ,  131  and fast imbalances  311 ,  321 , relative to one another, remains unchanged. Adjustment of the medium-speed imbalances  211 ,  221 ,  231 , relative to the others, is made possible by swivel motor  5 . 
         [0038]    In the embodiment according to  FIG. 7 , the ratio of the speeds of rotation of shaft groups  1 ,  2 ,  3 , relative to one another, amounts to approximately 1:2:3; the static moment of the shaft groups  1 ,  2 ,  3 , relative to one another, amounts to essentially 100:16.64:3.68. 
         [0039]    Using the aforementioned and claimed ratios of the speeds of rotation and the static moments, respectively, relative to one another, a very effective force effect in the forward drive direction can be achieved. This effect can be achieved even with a slight change in the ratio figures in the range of up to ten percent, but some efficiency is lost. Such modifications of the ratios of the speed of rotation and the static moments, respectively, relative to one another, are also considered to be part of the invention. 
         [0040]    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.