Conveyors: power-driven – Conveying system having plural power-driven conveying sections – With condition responsive control of a section
Reexamination Certificate
1999-07-22
2001-05-08
Bidwell, James R. (Department: 3651)
Conveyors: power-driven
Conveying system having plural power-driven conveying sections
With condition responsive control of a section
C198S460100
Reexamination Certificate
active
06227351
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transport system. From German Patent DE 40 39 265 C2, a transport system is known in which the feeding and/or discharging of workpiece carriers at machining units is performed with the aid of a phased conveyor. The conveyor belt of the phased conveyor is divided by cams into segments in which workpiece carriers are disposed. There are workpiece carriers with unmachined or machined parts and/or component units in the segments upstream and downstream of the machining unit, respectively. The conveying is done in accordance with a speed profile that recurs once per phase. This serves to increase the throughput of workpiece carriers. A speed profile can be shown for instance in the form of a speed and travel graph or a speed and time graph. Beginning at the zero speed, the speed of the phased conveyor increases to a certain value and then returns to zero. The speed profile for the phased conveyor is generated by a frequency inverter, a braked rotary current motor, a worm gear, and a disk cam gear. With the frequency inverter, the braked rotary current motor is operated at different but in each case constant rotary speeds, or rpm. The worm gear converts the rpm of the rotary current motor into a lower driven rpm. Such a gear is required in all transport systems that use rotary current motors, since the rotary speeds of a rotary current motor are relatively high. It is the disk cam gear that for the first time converts the constant driven rpm of the worm gear into a driving rpm for the phased conveyor, and this driving rpm is directly proportional to the speed profile.
During the machining cycle, the phased conveyor is at a standstill. It conveys articles only whenever the end of machining is reached and the outlet is empty. It is always disadvantageous, however, if after the machining there are no workpiece carriers at the inlet. Either the phased conveyor conveys an empty segment, which means that in the machining unit the parts and/or component groups of a missing workpiece carrier are machined, or the phased conveyor stops because it is waiting for an unmachined machining unit. During this period, no workpiece carriers are discharged. In the workpiece carrier throughput, a gap has occurred that can no longer be made up for.
Employing the principle of the phased conveyor to the entire transport system including the main conveyor way and the feeder conveyor way and discharge conveyor way would mean that the individual machining units would no longer be connected to a flexible transfer system but would be firmly chained together. This is because in that case the workpiece carriers would be trapped between cams or within segments and could thus no longer be transported flexibly.
The length of the phased conveyor is also an integral multiple of the length of one segment, which means that the length of the phased conveyor cannot be designed to be highly variable.
In addition to the known transport system, there are still others that in order to achieve a higher workpiece carrier throughput operate at a higher conveyor way speed. This has the disadvantage, however, that workpiece carriers run up at the correspondingly higher speed against stoppers or workpiece carriers that are at a stop. Thus dampers or additional time are required to calm the workpiece carrier, and once again this causes delays.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a transport system which eliminates the disadvantages of the prior art.
In keeping with these objects, one feature of present invention resides, briefly stated, in a transport system which has at least one conveyor means; at least one drive mechanism assigned to each of the conveyor means and driving the later; at least one electronic control unit provided for at least one drive mechanism and generating at least one speed profile which begins at a basic value other than zero, assumes at least one other value, and then resumes the basic value, so that the at least one conveyor means constantly convey workpiece carriers, the at least one conveyor means having at least one signal transducer whose signals act on the at least one control unit, so that the speed profile is tripped when a workpiece carrier reaches the signal transducer or a position at a machining unit, or when a machining unit reports an end of machining.
When the transport system is designed in accordance with the present invention it has the advantage over the prior art that workpiece carriers can be conveyed even during machining. If there is no workpiece carrier at the inlet, a workpiece carrier with machined parts and/or component units can still be carried away. However, since as a rule a plurality of workpiece carriers are always located upstream of the machining unit, the parts and/or component units of the workpiece carriers that are present can still be machined even if no new workpiece carrier has arrived at the inlet, and the workpiece carriers can be discharged after machining.
One important advantage of the transport system of the invention is that it can be used not only for machining units but also at other transfer points, such as node points; this considerably reduces the time for transferring one workpiece carrier from one conveyor way to another, while preserving the flexibility of the transport system.
Another advantage is considered to be that the speed profile for conveying the workpiece carriers can be set arbitrarily, since it is not created by a disk cam gear but rather by an electronic control unit, such as a frequency inverter. Thus speed profiles adapted to various situations can be set. For instance, in a given situation as a workpiece carrier is being discharged from a node point, a first speed can be approached initially and then this speed is maintained over a relatively long distance. Upon approach to a separator, the speed can be reduced, so that the workpiece carrier arrives at the separator virtually without any impact. A machining unit can follow shortly downstream of the separator. For this shorter distance, the workpiece carrier will then be transported at a further speed profile adapted to the distance.
Compared with the prior art, neither disk cam gears nor brakes are present, so that the attendant costs are also saved.
Since the length of the conveyor way does not depend on segment length, it can be designed highly variably.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4112999 (1978-09-01), Gasper
patent: 5186308 (1993-02-01), Munro
patent: 5228558 (1993-07-01), Hall
patent: 5477117 (1995-12-01), Saito
patent: 5979636 (1999-11-01), Vanacore et al.
Bidwell James R.
Robert & Bosch GmbH
Striker Michael J.
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