Conveyors: power-driven – Conveyor section – Reciprocating conveying surface
Reexamination Certificate
1999-08-03
2001-05-29
Ellis, Christopher P. (Department: 3651)
Conveyors: power-driven
Conveyor section
Reciprocating conveying surface
C198S768000, C198S750500
Reexamination Certificate
active
06237748
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to an oscillatory drive unit for use in an oscillating system to be oscillated substantially at the resonance point of the oscillating system. The oscillating system generally includes a mass to be oscillated which mass is resiliently suspended on or supported by a countermass by means of any kind of resilient springs. Although the invention has particular utility in connection with oscillating conveyors that are to be operated substantially at their resonance point, the problems to be solved with the object of the invention mainly occur also in other oscillating systems that primarily operate within the resonant range.
In prior art oscillating conveyors, the resiliently supported oscillating or conveying bodies are subjected to a forced oscillation by means of a vibrator. This oscillation causes the material situated on the oscillating conveyor to travel along the conveyor. There exist so-called oscillating conveyors that are subjected to an essentially linear oscillation, the direction of which approximately corresponds to the initial angle of a parabola. Such oscillating conveyors are frequently supported in resilient fashion on leaf springs that are arranged perpendicular to the desired oscillating direction and allow a practically linear oscillation in this direction. This practically linear oscillation only deviates from linearity due to the circular arc path of the spring ends. This deviation may be neglected if the difference between the oscillation stroke and the length of the spring is sufficiently large.
In addition to electromagnetic vibrators, it is also possible to utilize piston vibrators that are pressurized with compressed air as oscillatory drives for such oscillating conveyors. The latter provide the advantage that their oscillating behavior can be better adapted to different requirements.
With respect to the expenditure of energy, it is most favorable to operate oscillating conveyors within the resonant range. Within this range, the size of the masses to be moved is inconsequential. It simply must be ensured that the energy consumed by the damping in the springs and by the moved material is replaced. In this case, only part of the weight of the material to be conveyed consumes energy. Resonance conveyors are preferably realized in the form of conveyor chutes. With respect to the operating requirements, it is, however, disadvantageous that the resonance frequency of a system depends on the respective load of the material to be conveyed and varies accordingly. In known systems, the adaptation of a resonant drive to the resonance frequency of a system represents an almost insurmountable problem. An adaptive variation of the excitation frequency during the operation of such a conveyor can only be realized with significant expenditures. Consequently, measures of this type are frequently relinquished, and the oscillating resonance drives are designed in such a way that the operating range is displaced into the ascending part of the resonance curve, i.e., far away from the resonance apex. In this case, at least part of the resonance amplification can be utilized, and a damping of the amplitude while the system is subjected to a load may, for example, be compensated due to the fact that the resonance point is simultaneously displaced to a slightly lower frequency and the fixed operating frequency is displaced into a region of higher amplitude.
Even when using a more flexible piston vibrator, the adaptation of its frequency to the resonance frequency of a system is only possible under certain conditions. In piston vibrators, the power essentially depends on the piston diameter. However, the frequency and the oscillation amplitude result from the piston weight. If a heavier piston of the same diameter is used, the oscillation amplitude is correspondingly increased and the frequency is correspondingly decreased. This applies to cylindrical as well as stepped or differential pressure piston vibrators. In order to alter the oscillating behavior of a piston vibrator, pistons with different lengths and identical diameters are frequently utilized so as to attain different moments within the same power range. Normal piston vibrators that are coupled to a system to be subjected to oscillations usually comprise a piston without a piston rod which only moves back and forward within the vibrator housing. However, it is also possible to provide one side of the piston with a piston rod that extends out of the housing. The one-sided effect of this piston rod, which reduces the piston surface, makes it necessary to realize this vibrator in the form of a differential pressure piston vibrator. The piston rod that extends out of the housing may be additionally provided with masses that reduce the frequency. An adaptation of the frequency of a piston vibrator to the resonance frequency of a system would only be possible by lowering the air pressure. However, the power of the piston vibrator varies exponentially with the frequency, i.e., this measure can generally be precluded. In conventional systems, the springs of a resonance conveyor are usually designed in such a way that the resonance frequency of the system lies within the economical operating range of a certain vibrator type. This may, for example, be realized by altering the piston mass.
Resonance conveyors are not only sensitive to load changes. The natural frequency essentially also depends on the ratings of the springs used and, for example, the weight of the conveyor. If the conveyor is structurally modified such that its weight is changed, it is possible that the conveyor no longer resonates and consequently conveys no material. In conventional so-called oscillating resonance conveyors that operate at a frequency of only approximately 85% of the resonance frequency, it is a customary procedure to operate below this frequency in order to still attain a noticeable resonance amplification of the oscillation amplitude and reduce the sensitivity of the system. If a conveyor that is correctly calculated and designed with respect to its resonance frequency is assembled on a foundation or frame that is insulated against oscillations, i.e., assembled elastically, so as to transmit the least possible oscillations onto the substructure, the mass of the foundation and its elastic support must be incorporated into the calculation, i.e., a system, the drive of which is generally adapted to the resonance frequency, no longer resonates.
The present invention is based on the objective of developing an oscillatory drive for a system with an oscillating mass and, in particular, an oscillating conveyor, in which the oscillatory drive practically recognizes the respective resonance frequency of the driven system, follows changes of this resonance frequency, and supplies the system with the energy required for maintaining the oscillations without electrical recognition or control units.
According to the invention, this objective is, in principle, attained with the characteristics disclosed in the characterizing portion of claim
1
.
Although a person skilled in the art will easily ascertain that the invention can also be utilized in other oscillating systems, e.g., vibration tables, screens, filter frames, etc., the invention is described below with reference to a resonance conveyor.
Leaving aside the corresponding coupling of the individual elements, it is an essential aspect of the invention to provide an oscillatory drive, the mutually moving components of which are not positively limited with respect to their mutual oscillation amplitude, e.g., by means of a limit stop, but rather able to essentially freely adapt to a resonance oscillation of the system. In this case, it is not precluded that a certain (progressive) elastic limitation for the mutually oscillating parts is provided. Consequently, the times at which the drive supplies energy are not dependent on the reversal points of a drive component, e.g., a piston. On the contrary, the energy may be supplied at an interim phase during th
Crawford Gene O.
Ellis Christopher P.
Lee Mann Smith McWilliams Sweeney & Ohlson
Netter GmbH
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