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Ch42-I044963.fm Page 204 Tuesday, August 1, 2006 3:57 PM
Ch42-I044963.fm
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204 Page 204 Tuesday, August 1, 2006 3:57 PM
SCHEDULER DRIVEN MODIFICATION OF PROCESS PLANS

Modification Process of Process Plans

In the newly proposed method, the constraints on the machining equipment are sent to the job holons as the feed
back information of the scheduling results, to generate the modified sequences of the machining equipment for the
individual job holons. Tt was found that the machining process in some of the machining equipment are
concentrated where as the other machining equipment is remaining idle. Therefore, the global objective functions,
such as the total make span and the weighted tardiness cost, can be improved, if the scheduling holon redistributes
the concentrated load of the machining processes to the other machining equipment and reduces the waiting time.
The process plan modification procedure basically consists of two stages, they are, the load balancing of the
machine equipment by the scheduling holon and the modification of the sequence of the machining equipment by
the job holons.

Load Balancing
The load balancing means here to reallocate all the machining features and their machining processes to the
suitable machining equipment, in order that the load of all the machining equipment is well balanced, taking into
for the machining features.
consideration of the entire alternative machining equipment MEA ijp
The following steps are being taken during the load balancing.
STEP 1 Generation of load chart: The load chart of all the machining equipment is drawn based on the scheduling
results.

STEP 2 Calculation of average balanced load: The average balanced load (ABL) is estimated from the load chart,
based on the following equation.

ABL= SEMAT^/N (1)

where, i is ID of the job holon,/ is ID of the machining features machined by the j-th position in the machining
sequence, k is ID of the process plans of the job holon i, which is selected in the scheduling process and N is total
number of machining equipments.

STEP 3 Selection of machining equipment to be reallocated: The machining equipment with the maximum load is
selected, which is reallocated first. The reallocation process is carried out step-by-step from the machining
equipment with large load in the load chart.

STEP 4 Reallocation of machining features to selected machining equipment: The machining features are
reallocated to the machining equipment selected in the STEP 3. The LPT (Longest Processing Time) rule is used
in the research to determine the machining features to be loaded to the selected machining equipment. By the LPT
rule, the highest priority is given to the machining features with the maximum value of the machining time
MATj®. Therefore, the machining features with the high priorities are allocated to the selected machining