MAS Expert Agent Operational Strategy

The MAS Expert Agent is defined as the expert of MAS configuration and performs two assessments in the configuration process: the expert configuration assessment and the performance failure assessment which were defined in chapter 5. Despite this division, the internal operation of the MAS Expert Agent is quite similar, since it is based on the existence of patterns and rules for both assembly process configuration and physical system configuration. Therefore any assessment of the

MAS Expert Agent covers two sub assessments, the assembly process assessment

and the physical assessment. As it was stated before, this agent only contains a lightweight set of rules that demonstrates the agent potential in the configuration methodology once more knowledge can be acquired and incorporated into the agent. The operational behaviour of the MAS Expert Agent for the expert configuration assessment firstly looks at the completeness of the given solution. The completeness of a solution assessment is performed in phases. The first looks at predefined system completeness rules and is followed by the matching with internal patterns for MAS solutions. The decision of looking firstly to the rules resides in the fact that these can provide early insight into missing elements in the solutions using minimal effort. This follows the smallest effort and biggest impact approach, therefore the rules act as the first tier for the completeness assessment. The rules have to be absolute and

157 cannot have any conflicts, while the patterns provide the means to have parallel solutions.

The rules for the completeness assessment look at both physical aspects and assembly processes aspects. A set of very basic rules for completeness assessment are proposed as follows to provide an overview of the impact that these might have in the configuration methodology:

· Incomplete physical interfaces – The existence of non plugged physical ports that are not indicated as optional requires the establishment of requirements based on the global interface definitions where the matching port pair or pairs are defined.

· Incomplete assembly process parameter interfaces – The existence of mandatory parameters for an assembly process that are not connected due to the absent matching parameter port.

If these rules are not breached, that is, if the solution follows the rules, the MAS Expert Agent performs the matching of existing patterns to the given solution. Because this is viewed as an evolving agent, in the absence of patterns, as in the absence of rules, the agent simply assumes that the solution is valid. The patterns allow for the definition of alternative configuration patterns that indicate what the necessary elements in a configuration are. The ability to have alternatives is crucial because the rational is that the solution needs to follow one of the given set of patterns, and if it does not, the missing element or elements of the closest match should be established as missing requirements. The patterns can be both physically related and assembly process related. Figure 6.13 provides a conceptual overview of pattern structures that the MAS Expert Agent contains. If any pattern exists then the solutions would be required to fulfil at least one of the defined variants.

158 Figure 6.13 - Conceptual Overview of Pattern Structures

It is also proposed that the predefined patterns structure cater for definitions that allow for defining mandatory components of the given variant, while others are merely optional. This characteristic provides the system with the ability for not very complex definition since the only constraint that the MAS Expert Agent imposes is the fact that all alternative patterns need to exist otherwise possible valid solutions might be disregarded. The model provided in chapter 4 can cater for this description with a small enhancement for dealing with variants, thus it is proposed its use. The other assessment performed by the MAS Expert Agent is the perform failure assessment as defined in chapter 5. The introduction of this assessment is supported by the possibility that certain failures in solutions can be compensated, namely the MAS repeatability and cycle time. However the form on how to compensate the failure of these is expert knowledge that requires a wide understanding of MAS. It is proposed that the MAS Expert Agent contains a set of rules that indicates how a given failed configuration can be salvaged, or if in fact it is impossible. To

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159 establish these rules one needs to look at the assembly characteristic at fault and find the source of the problem. While for cycle time the source is normally a bottleneck, the repeatability is more of a stacking up problem. Therefore the rules for dealing with these two aspects are quite different and require a separation. So the first thing the MAS Expert Agent needs to assess is the type of failure, and verifies if rules exist to compensate for this error. The power consumption which is associated with the running cost of the system and accuracy do not have rules to compensate for it. Nevertheless a future iteration of this agent might provide extra definition of rules for these aspects. For this work it is proposed two sets of rules, one for compensating for cycle time, and another for repeatability.

The proposed rule for dealing with the cycle time failure is quite straightforward, if the bottleneck station cost is inferior to the maximum cost minus current cost, then requirements for a parallel station are formulated, otherwise there is no means for compensating.

The proposed rule for dealing with repeatability needs to look at the type of assembly processes being performed. In chapter 4 a classification for process types was introduced and it is used for the implementation of this rule. The only way one can compensate for error is before the fixating processes, since after these, the error is permanent. Therefore these processes need to be found to determine which ones produced the biggest error impact to the solution. Once these are identified, the MAS

Expert Agent establishes new requirements for a qualifying process that should

occur before the fixating process with most impact. However this qualifying process needs to occur when compensation can still occur, as such it should be placed before the previous handling process.

In the event of multiple failures, that are both aspects failed, the approach of the

MAS Expert Agent is to verify cycle time first, since it is the rule that is more likely

to not produce compensation options. The rules are internal to the agent, however it is expectable that in the future a rule engine should be incorporated into this agent.

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