Electrical computers and digital processing systems: support – Synchronization of clock or timing signals – data – or pulses
Reexamination Certificate
2000-03-15
2003-10-14
Gaffin, Jeffrey (Department: 2185)
Electrical computers and digital processing systems: support
Synchronization of clock or timing signals, data, or pulses
C706S010000, C355S133000
Reexamination Certificate
active
06633990
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a time scheduling method for a modular engine, and more particularly to such an engine including a set of action modules each for performing a particular action, wherein, for a chain of actions to be scheduled, interaction between the modules involved in the chain of actions comprises an output from one module being delivered as an input to another module, the engine comprising at least one module that does not need an input from another module for performing a first action, the engine performing a method comprising the allocation of a time to each action to be performed by the modules on the basis of information on the current status and timing constraints of the respective modules. The invention also relates to a scheduler employing this method and to a sheet handling machine, e.g. a copier, scanner or printer including such a scheduler.
BACKGROUND OF THE INVENTION
In a modular engine it is necessary to coordinate the functions of the various modules by establishing a time schedule according to which the various actions of the modules are to be performed.
U.S. Pat. No. 4,737,907 discloses a multiprocessor control system for a xerographic machine having a modular architecture. Each module is controlled by its own processor, and coordination of the various functions is achieved by a master processor communicating with the control processors of the modules via a bus system. Synchronizing signals, among others a machine clock signal, can be applied to the various processors independently from the bus system. Thus, it is possible for the master processor to download instructions to the control processors of the modules, such instructions specifying the action to be performed, an event by which the action is triggered, and a delay time between the triggering event and the moment at which the action has to be performed.
This has the advantage that the control processor of the module can autonomously monitor the triggering event and execute the required action at the correct timing, so that the burden on the master processor and the bus system is reduced. The triggering events and the delay times which together establish a time schedule are determined by the master processor.
A scheduling method according to the preamble of claim 1, for a modular print engine, is disclosed in European Patent application having publication no. EP 747793. The modules of the engine are in this case formed by the various subassemblies of the printer, such as paper storage tray, a sheet feeder, a paper conveyor, a printing device and the like. These modules interact in that a paper sheet is passed through the engine from module to module. The scheduler determines the modules needed for a given task and establishes a sequence of actions on the basis of models representing the functions of the various modules.
In order for the modules to cooperate without timing conflicts, it is generally required that all the timing constraints of the various modules have to be taken into consideration in the scheduler. As a result, the conventional scheduler is relatively complex, and difficulties or errors are likely to occur when the system configuration is changed, i.e. by adding, removing or replacing individual modules.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a scheduling method and a scheduler which permit a high variability in the engine configuration and are robust against alterations of this configuration.
According to the invention, this object is achieved by a scheduling method performed by a modular search engine, wherein each module allocates the timings for its own actions by sending a timing offer to the module to which the output is to be delivered and receiving from that module a message accepting or rejecting the offer, the timing offer being based on the internal status and timing constraints of the module itself and, if an input from an other module is needed, on a timing offer from that module.
The scheduling process is highly decentralized, so that the modules practically act as autonomous entities which negotiate the time schedule among each other. Most importantly, each module only needs to have information on its own functionality, status and timing constraints and on the type of interaction with other modules. From the view point of an individual module, the status or the timing constraints of other modules are irrelevant. This has the advantage that the internal configuration of each module may be altered as desired, and it is not necessary to notify these alterations or their consequences to other modules or to a central controller. As far as the scheduling process is concerned, the alterations of the internal configuration will only be reflected by the timing offers sent to the other modules, and, as a consequence, the other modules only have to react on these timing offers in the usual way without having to know the alterations that have been made.
As a result, the scheduling method offers high flexibility in the engine configuration and is at the same time of a general applicability so that it can be used for a large variety of engine types and engine designs.
The term “module” as used herein refers not only to the engine subassemblies performing the task of the module but also to the associated control system which itself may be formed by hardware and/or software. Of course, it is the control system of the module that determines and sends the timing offer to the control system of another module, whereas it is the engine subassembly that delivers the output, e.g. a copy sheet, to an other engine subassembly. It is also noted that the term “chain” should not only be interpreted as a flow from one start point to one end point, but also includes several flows coming together or splitting up.
When it was stated above that the scheduling process is “decentralized” this is meant primarily in a logical sense and not necessarily in a physical sense. Thus, it is possible within the scope of the invention that the control systems of the various modules are centralized in a single multi-processor control unit or even in a single processor. In the latter case, the control functions of the modules are implemented as software modules or subroutines. Then, when a module, i.e. a system subassembly is altered or replaced, this implies that the associated subroutine is also altered or replaced.
As an alternative, it is of course possible that the control systems of the various modules are configured as separate control units or processors which communicate with each other via a bus system. In this case, the control unit of an individual module may also be physically integrated into the corresponding engine subassembly. As an example, consider a sorter or a stapling device that is connected to the paper output of a copier and that has its own control unit that is connected to the control unit of the copier.
In any case, the decentralized architecture has the advantage that maintenance and modification of the engine are greatly facilitated because the necessary interventions in the hardware and/or software of the scheduler are determined in a natural way by the structure of the modules and their interactions.
The invention further has the advantage that the scheduling process is inherently safe, because each timing offer has to be either accepted or rejected by the receiving module. This implies that the receiving module has to check whether the offered timing would lead to a conflict. As a result, a timing error will lead to a rejection of a timing offer and hence to a failure of the scheduling attempt but not to any damage to the engine subassemblies.
The requirement that at least one module of the engine does not need an input from another module for performing a first action guarantees that the scheduling process will not be circular. The scheduling process can always be started with the module which does not depend on an input from another module so that all the information needed for issuing a timing offer is available in this
Birch & Stewart Kolasch & Birch, LLP
Gaffin Jeffrey
Oce--Technologies B.V.
Wang Albert
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