Conveyors: power-driven – Conveyor arrangement for selecting among plural sources or... – With selection responsive to means containing or introducing...
Reexamination Certificate
1998-07-28
2003-09-23
Valenza, Joseph E. (Department: 3651)
Conveyors: power-driven
Conveyor arrangement for selecting among plural sources or...
With selection responsive to means containing or introducing...
C198S358000
Reexamination Certificate
active
06622845
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention pertains to a transport system and to a method for controlling the transport system. Such transport systems are used in the fabrication of wafers in the semiconductor field and they are an essential part of the production and automation concept.
Conventional transport systems, which are known as trolley systems, for example, have numerous disadvantages. One of the more significant disadvantages of the prior art systems resides in the fact that it is possible to expand or change the transport paths only with a high outlay, and that the control operates in a manner that is quite susceptible to faults. These disadvantages may be ascribed, inter alia, to the fact that a superordinate control unit is responsible for all the data that arise, and that the transport system is provided with too few control points which could enable monitoring of the individual trolleys. In the event of a fault, fault propagation occurs and can lead to a failure of the complete transport system and an attendant breakdown on account of the small number of control points and on account of the extensive system communication which has to be processed by a superordinate control unit.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a transport system and a control method for controlling the transport system, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which ensures the robustness of the system and the remainder of the system continues to operate in a dependable manner even in the event of a fault or the failure of individual components.
With the foregoing and other objects in view there is provided, in accordance with the invention, a transport system for transporting a multiplicity of individual items, comprising:
a multiplicity of conveying devices for transporting individual items;
a multiplicity of branching devices connected to respective conveying devices for selectively branching the items to different conveying devices;
a multiplicity of processing devices for processing the items, the processing devices having inlets and outlets connected to respective conveying devices;
a multiplicity of storage devices for temporarily storing the items;
an information medium attached to each item for storing at least one first destination address identifying a specific processing device to which the respective item is to be transported;
a writing device at each outlet of a respective processing device for writing a second destination address after a processing operation and upon transferring the item to a respective conveying device; and
each branching device reading the information medium of each item and utilizing an internal destination address list to define a branching direction for the respective item.
In other words, the transport system is used in particular to transport wafers and it comprises a multiplicity of carrier devices which accommodate the wafers, a multiplicity of conveying devices, which transport the carrier devices, a multiplicity of branching devices, which branch the carrier devices to different conveying devices, a multiplicity of inlets and outlets (lifts) at processing devices, at which the wafers are processed, and a multiplicity of storage devices, in which the carrier devices with the wafers are temporarily stored. Each carrier device has an information medium, in which at least one first destination address is stored, with the result that the associated wafers can be transported to a specific processing device corresponding to this destination address. The first destination address is read at each lift at a processing device, and a second destination address is written after the processing operation by the lift, and each branching device uses an internal destination address list to define the branching direction in that the information medium of each carrier device is read at each branching device.
In accordance with an added feature of the invention, the second destination address corresponds to a production area, the item to be transported being processed at the first destination address and then transported to a first storage device of this production area.
In accordance with an additional feature of the invention, if the first storage device of this production area is occupied, the item to be transported successively selects all the other storage devices of this production area until a free storage location is reached.
These features serve the purpose of independent control. The transport organization is thus executed at a lowest control level of the transport system.
In accordance with another feature of the invention, the item is transported in a circle in the afore-mentioned production area if all the storage devices are occupied. This has the effect that the conveying devices themselves are used as temporary stores for the items.
In accordance with a further feature of the invention, the destination address lists in each branching device are set up in a specific manner and include all the destinations which can be reached via the specific branching device. In accordance with again a further feature of the invention, the destination address lists include only the destinations which cannot be reached in a preferred direction of the branching device. This results in optimization of the address lists so that, on the one hand, their size is kept small and, on the other hand, alternative routes can nevertheless be traveled.
In accordance with again an added feature of the invention, a further improvement in route planning is afforded where each branching device additionally takes account of the activities of neighboring branching devices when the branching direction is determined, in order to optimize the transporting path. In analogy to traffic control, transport paths which are already severely loaded can be circumvented.
In accordance with again an additional feature of the invention, the content of the information medium on the item is nonvolatile. The destination addresses are thus retained and the transport task can be resumed even after a power failure.
In order to be able to react suitably to exceptional situations, according to again another feature, the transport system comprises additional address lists in each branching device, which address lists can be activated in exceptional situations, such as fire alarm, deactivation of the transport system and partial deactivations of the transport system. Furthermore, the destination address lists and the additional address lists may be continuously updated in order constantly to register changes in the set-up of the transport system.
Transport reliability may be further improved, in accordance with additional features of the invention, which ensure that transport tasks which are en route for an exceptionally long time are ascertained, in which case a transport task is begun by removal of the item from the storage device, the destination addresses are written to the information medium of that item, the item is transported by means of the conveying devices and is branched in the direction of the first destination address by means of the branching devices, processing being carried out after the processing device corresponding to the first destination address has been reached, and then the item is provided with the second destination address in order to be transported further. If the time interval between removal from storage and processing is longer than a predetermined time period, the item is placed onto a fault list.
In order to unambiguously identify the item to be transported, each item is allocated a specific number which is likewise stored in the information medium, this number being entered in the above-mentioned fault list.
With the above and other objects in view there is also provided, in accordance with the invention, a method of controlling a transport system which comprises the following steps:
removing an item to be transported from a storage device;
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Heinrich Harald
Odrich Falk
Österreich Peter
Recklies Jörg
Welzk Andre
Siemens Aktiengesellschaft
Valenza Joseph E.
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