1. Field of the Invention
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.
2. The Prior Art
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.
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.
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.